I originally developed this recipe for ChocZero using their vanilla syrup, and I've been making it pretty much weekly since then. The syrup adds the liquid that binds everything together, so this isn't your typical mug cake with eggs and milk. It's simpler than that, and the texture lands somewhere between a biscuit and a sponge cake.
The first bite is warm blueberry juice soaking into buttery cake, and that's what keeps me coming back. I've tried other blueberry mug cake recipes that use eggs or cream cheese, but they come out rubbery. This one stays soft because the syrup does double duty as sweetener and binder.
If you don't have vanilla syrup, one reader (Marie) swapped in Greek yogurt with a little extra sweetener. I asked her about the texture and she said it was denser but still good. I've since tested it myself and she's right. The yogurt version is more like a blueberry cobbler than a shortcake, which is its own kind of great.
This is a true single-serving dessert. 6.8g net carbs for the whole thing, and it takes about five minutes from bowl to first bite. I eat it straight from the ramekin most nights, but if I'm having people over, I flip it onto a plate and add something on top. A keto chocolate mousse alongside it is ridiculous in the best way.
I keep coming back to this for weeknight desserts because there's no baking time, no preheating, no dishes beyond one bowl and one mug. On days when I want something more involved, I'll make my birthday mug cake, keto pumpkin dump cake, or keto strawberry shortcake kebabs for a crowd. But for a Tuesday night after dinner, this is the one.
The keto baking community has figured out that almond flour plus a little coconut flour creates the best crumb for mug cakes. Pure coconut flour absorbs too much liquid and goes chalky. Pure almond flour can be too dense. The blend I use here (2 tablespoons each) hits the sweet spot.
One thing I want to flag: the coconut flour matters here. If your coconut flour is old or has been sitting open, it absorbs differently. I've had batches come out dry because of stale coconut flour. Fresh, sealed coconut flour makes a noticeable difference in how the batter holds together.
Low Carb Blueberry Mug Cake
Sweet and soft, this is the keto dessert I reach for when I want something warm and real without turning on the oven. The first bite is all fresh blueberry juice and buttery cake, and it only gets better as you work through it.
Since it’s made in a single mug, it’s naturally portion-controlled. The total net carb count is just 5 grams, so I get a proper dessert without wrecking my macros.
Berries are one of the best fruits for low carb eating. Fresh blueberries have slightly more carbs than raspberries or strawberries, but they still fit just fine. They clock in at 12 grams of carbs per 100 grams (about 3 small handfuls). I use 8-10 blueberries in my mug cake, which comes out to 1-2 grams of net carbs for the whole thing.
I’ve tested this with raspberries and blackberries too. Both work, but blueberries give you the best flavor burst when they heat up in the microwave. They almost pop and release this warm jam-like juice that soaks into the cake. That’s what makes this version my favorite.
Best Flour Blend for This Shortcake
I use a mix of almond flour and coconut flour to keep the carbs low and the texture right. If you need a nut-free option, sunflower seed flour swaps in cup for cup with almond flour. I use the same flour logic in my almond flour cookies.
Don’t use coconut flour alone. It’s incredibly absorbent and will turn your cake into a dry puck. I learned this the hard way early on. The almond flour provides moisture and richness while the coconut flour lightens the crumb. If the batter feels too thick, add a splash of water or almond milk to loosen it up.
How to Microwave a Mug Cake
Microwave for 1 minute in a standard 800-watt microwave. If yours runs at 900-1000 watts, start with 50 seconds and check from there. Stick a spoon in the center. If the batter is still wet, go another 10 seconds. I’d rather pull it out slightly underdone than let it go too long, because an overcooked mug cake turns rubbery fast.
If you don’t have a microwave, bake at 350 degrees for 8-10 minutes in a ramekin. I’ve done this and it works well, just takes longer. When it’s done, add a dollop of whipped cream and eat it right from the dish.
Mug or Ramekin?
I prefer a ramekin over a mug. The wider shape means the batter cooks more evenly, so you don’t end up with a raw center and overcooked edges. Use an 8-ounce ramekin or larger.
If you’re baking in the oven instead of microwaving, always use a ramekin. Glass mugs can crack at oven temperatures. Either way, spray the inside with cooking spray or rub it with a little oil so the cake releases cleanly when you flip it out.
Tips for the Best Results
Don’t overmix the batter. A few lumps are fine. Overmixing activates too much structure from the coconut flour and makes the cake dense instead of tender.
If you’re using frozen blueberries, thaw them first and drain the excess juice. Otherwise the extra liquid throws off the batter ratio and you’ll get a soggy bottom.
For a lemon blueberry twist, I add a tablespoon of fresh lemon juice and a teaspoon of zest to the batter. It brightens everything up. If you like fruity desserts, my keto raspberry no-bake cheesecake is another one I come back to.
How to Make Keto Blueberry Shortcake in a Mug
Combine almond flour, coconut flour, melted butter, vanilla syrup, baking powder, and salt in a bowl. Drop blueberries into a greased ramekin or mug, spoon the batter on top, and microwave for 60 seconds. I pull mine when the top still looks slightly wet because it finishes cooking from residual heat.
Mix together almond flour, coconut flour, vanilla syrup, butter, baking powder and salt in a small bowl. Set aside.
2
Add blueberries
Spray cooking spray into a large ramekin or microwave safe mug. Add blueberries to the dish.
3
Top with shortcake batter
Scoop shortcake mixture to the top of the blueberries. Microwave for 1 minute. Serve with homemade whipped cream or ice cream.
Nutrition
Per serving: Whole recipe
Calories
251
Fat
20.1g
Protein
5.1g
Total carbs
13.7g
Net carbs
6.8g
Nutrition is an estimate calculated from the ingredients listed. Brands vary, so check labels if you track closely.
Frequently Asked Questions
Can I use frozen blueberries instead of fresh ones?
I've made this with frozen blueberries plenty of times. Thaw them first and drain the liquid, otherwise your batter gets too wet. The flavor is almost identical to fresh, maybe even a little more intense since frozen berries release more juice when they heat up.
What can I substitute for the almond flour?
I've tested sunflower seed flour as a 1:1 swap and it works great for a nut-free version. The texture is nearly identical. A low carb all-purpose blend works too, but I find the crumb is slightly different. If you go that route, start with the same measurement and add a splash of liquid if the batter seems dry.
What microwave wattage works best for this mug cake?
I use an 800-watt microwave and 60 seconds is my sweet spot. If yours runs hotter (900-1000 watts), start at 45-50 seconds. I overcooked this exactly once at high wattage and the whole thing went rubbery. Underdone is always better than overdone with mug cakes.
How do I know when the mug cake is done?
I stick a spoon in the center. If it comes out clean or with just a few moist crumbs, it's ready. The top should look set and slightly springy. I pull mine when it still looks a tiny bit wet on top because it keeps cooking for another 20-30 seconds from residual heat.
How do I prevent the blueberries from sinking to the bottom?
I toss my blueberries in a pinch of coconut flour before dropping them in the mug. The light coating gives them something to grip so they stay suspended in the batter instead of settling. This works with both fresh and thawed frozen berries.
Can I add lemon zest or juice to this recipe?
I do this all the time. A tablespoon of fresh lemon juice and a teaspoon of zest turns this into a lemon blueberry version, and it's fantastic. The citrus cuts through the sweetness and makes the blueberry flavor pop even more. I add both directly to the batter before spooning it over the berries.
Can I double this recipe to make two servings?
I just make two separate mugs instead of doubling into one larger dish. A bigger volume doesn't cook evenly in the microwave, so you end up with raw spots in the middle. Two mugs side by side, 60 seconds each, and you're done. I do this when my husband wants one too.
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New to mug cakes, so sorry if this is obvious. I don’t have sugar-free vanilla syrup. Looks like it’s doing more than just flavor though. Sweetness and liquid too? Would vanilla extract work if I made up for the moisture somehow, or is the syrup kind of necessary?
Made this and it was genuinely good. But I had this low-key disappointment the whole time because shortcake in my head means layers, cold cream, the whole thing. Baking the blueberries right into the batter skips all that and lands closer to a blueberry mug cake. Still fine. Whipped cream on top would close the gap though.
Thank you for the feedback. It’s a single-serve mug bake, so it never gets split and layered the way a real shortcake does. That’s a fair thing to miss. The recipe card does call for whipped cream on top, and I’d make it cold and pile it on. Sweetened heavy cream, whipped stiff, takes about two minutes.
Somewhere around batch eight I stopped mentally prefixing this with ‘keto’ when I think about it. Just shortcake now. One honest note: the coconut flour shows a little on the first bite, slight graininess before the blueberries take over. Not enough to stop me, but I kept wondering if I was doing something wrong, so figured I’d say it.
The ‘just shortcake’ thing made me smile. That first-bite graininess is the coconut flour before it fully absorbs, not a you problem. I pull mine and let it sit 30-40 seconds and it smooths out.
Pull it at 50 seconds if your microwave runs hot. The shortcake keeps cooking after you stop it, and rubber vs. soft is just those last 10 seconds. Took me two rounds to figure that out.
Two rounds is fast, Valerie. I’ve done this with a 900-watt and even 55 seconds started pushing it. The mug holds heat so long you barely notice it crossed over until you’re already eating.
The butter-in-the-ramekin trick changed how I make this. I melt the tablespoon of butter right in the ramekin, swirl it around to coat the sides, then mix the batter directly on top. One fewer bowl and it slides out clean every time. I also started adding a teaspoon of heavy cream to the batter and the texture got more tender, less dense, closer to actual shortcake crumb. It’s been on rotation every afternoon this week because it’s too hot to even think about the oven, and 60 seconds in the microwave with jammy blueberries at the bottom is exactly what I needed. I flip it onto a plate, add a spoonful of whipped cream, and it looks like I put in actual effort.
Hadn’t let myself think about shortcake in months. Made this on a random Tuesday, five minutes, and it actually tasted like summer. Did not expect to get emotional about a mug dessert.
I pre-mix the dry ingredients in small jars on Sunday so I can throw one together any weeknight without measuring. One minute in the microwave and the blueberries go jammy under the cake. Fastest dessert I make.
Sunday jars are such a good idea for this. I end up re-measuring the coconut flour every single time because I always second-guess myself on the ratio.
If your mug is on the smaller side, use the ramekin instead. I tried a 12oz mug the first time and the batter barely had room to rise. The ramekin gives it enough space to puff up and the blueberries at the bottom get a little jammy from the heat.
Used frozen blueberries because I didn’t have fresh, and they release enough juice while cooking that you get this little syrupy pool under the cake. Thaw them for a minute first though or the batter takes longer to set in the middle.
Used frozen blueberries since that’s what I had, thawed with a squeeze of lemon juice before layering in. They released enough liquid during the microwave minute that there’s a jammy pocket at the bottom. Didn’t plan it, not complaining. The shortcake stays dry and slightly cakey on top while the blueberries underneath go saucy and warm. Two textures, one mug. My microwave runs hot so I pulled it at 50 seconds and the texture landed right. The lemon sharpens the blueberry flavor enough that it tastes like something you’d actually serve.
Lemon with frozen blueberries does something fresh can’t quite replicate. And yeah, 50 seconds if your microwave runs hot – I’ve overcooked this at 60 and the whole thing goes rubbery fast.
Made a batch of these for spring book club and the one woman who always brings the fancy bakery box kept looking at me like I’d been holding out on her.
Tried frozen blueberries straight from the bag and they actually work better than fresh. Enough juice cooks out to keep it from drying out. Don’t even bother thawing.
Made a round of these for a girls’ night last weekend as a little dessert-in-a-mug moment between courses, mostly because I could pull them together in under five minutes. My friend who has been on the fence about keto desserts picked hers apart looking for the catch, then quietly made herself a second one when she thought no one was watching. The blueberries at the bottom get almost jammy in the microwave, which I think is what got her. Keeping this one in the back pocket for whenever I need something that looks more intentional than it actually is.
One minute in the microwave and somehow the blueberries cooked into this little jam pocket at the bottom, first mug cake I’ve ever tried and I’m already wondering if it works the same with raspberries.
I’ve made this like five or six times now and I just figured out why mine kept turning out inconsistent (I’m still pretty new to all this keto baking stuff). The times I used frozen blueberries straight from the freezer, the juice kind of pools down into the shortcake as it cools and oh my god it’s so much better? Like it makes this little blueberry puddle at the bottom that the shortcake sits in and I didn’t even know I wanted that. I was using fresh blueberries the first few times and they’re fine but now I always keep a bag of frozen in the back of my freezer just for this. The one minute cook time still works even with frozen berries, which I wasn’t expecting. Going to try this with frozen raspberries next because I feel like that would be incredible.
Not draining creates the puddle on purpose now. I tell people to drain because wet batter is a real problem, but the jam pool at the bottom is actually better. Frozen raspberries next, yes.
The coconut flour is doing that. Most mug cakes are just almond flour and the texture never lands right. That combo is the whole reason this one works.
