Keto Vanilla Birthday Cake
Published July 29, 2025 • Updated February 21, 2026
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This keto birthday cake is fluffy, moist, and spongy with rich vanilla flavor and a creamy buttercream frosting. I built it with oat fiber and whey protein isolate so it actually tastes like real cake, not a dense, gritty low-carb substitute.
If you’ve been looking for a cake that actually tastes like the real thing (not cornbread, not a brick, not something you politely choke down in front of your low-carb friends), this is it. This keto birthday cake has a soft, fluffy crumb and sweet vanilla flavor you’d expect from a classic celebration cake, plus a vanilla buttercream frosting you’ll want to eat with a spoon. I’ll be honest, my chocolate cake usually steals the show around here, but after I served this at a family party, even my chocolate lovers were converted. It’s light, spongy, and doesn’t scream “I’m on a diet.”
What sets this apart from other almond flour cakes? The secret is in the texture, and trust me, that matters more than anything when you’re trying to recreate a traditional cake. Most keto cakes end up dense, dry, or greasy. I wanted this one to have bounce. Real, soft, cloud-like bounce. So I brought in two ingredients that changed everything: oat fiber and whey protein isolate. Oat fiber adds a zero-carb, delicate fluff factor (it’s the insoluble part of oat husks, not actual oats), and whey protein gives the cake structure and lift without weighing it down. Together they do what almond flour alone can’t: make a cake that feels light.
It took a few test rounds and a couple of tragic cake fails, but this final version is everything I wanted. It’s naturally gluten-free, has just the right amount of sweetness, and doesn’t rely on coconut flour or a dozen eggs to get the job done. If you’re into layer cakes, this base also works as a strawberry shortcake or paired with my ice cream cake for something extra.
The buttercream is just as important as the cake itself. I beat softened butter on its own for a full 4-5 minutes before adding the powdered sweetener, vanilla, and heavy cream. That sounds excessive, but it’s what makes the frosting fluffy and smooth instead of dense and greasy. I add the heavy cream a tablespoon at a time until I like the consistency. It pipes well, spreads easily, and holds up overnight in the fridge without separating.
Why this vanilla cake is worth baking
- Actually fluffy. Like boxed cake mix fluffy. No weird dense texture or dry crumb.
- No coconut flavor or gritty mouthfeel. I skip the coconut flour and lean into almond flour, oat fiber, and protein powder for a smoother bite.
- Zero weird aftertaste. I use sweeteners that don’t overpower the vanilla.
- Perfect for non-keto eaters. No one will know it’s low carb unless you tell them.
- Totally customizable. Use it as a base for chaffles, cupcakes, or layer cakes.
So go ahead, stick some candles in it. This one deserves it.
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Keto White Cake Ingredients
2 cups almond flour -
2 tablespoons oat fiber
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1/4 cup unflavored whey protein isolate
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1 tablespoon baking powder
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1/2 teaspoon salt
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6 egg whites, room temperature
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1/2 cup unsalted butter, melted
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1/3 cup plain Greek yogurt or sour cream
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1 cup sugar-free sweetener
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1 tablespoon vanilla extract
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1/4 cup unsweetened nut or seed milk
Double Batch Keto Vanilla Buttercream Frosting Ingredients
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2 cups unsalted butter, softened room temperature
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1 1/2 cups powdered sugar-free sweetener
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1 1/2 tablespoons vanilla extract
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1/4 cup heavy cream
Step by Step Instructions
Step by Step Instructions
Preheat oven & prepare cake pans
Preheat oven to 350°F. Line two 8-inch round cake pans with parchment and lightly grease the sides with butter. Set aside.
Mix dry ingredients
In a large bowl, whisk together almond flour, oat fiber, whey protein powder, baking powder, and salt. Set aside.
- 2 cups almond flour
- 2 tablespoons oat fiber
- 1/4 cup protein powder
- 1 tablespoon baking powder
- 1/2 teaspoon salt
Beat egg whites
In another large bowl, whisk the egg whites until slightly frothy, about 2 minutes.
- 6 egg whites, room temperature
Add remaining wet ingredients
To the egg whites, add melted butter, yogurt, sugar-free sweetener, vanilla, and milk of choice.
- 1/2 cup unsalted butter, melted
- 1/3 cup plain Greek yogurt or sour cream
- 1 cup sugar-free sweetener
- 1 tablespoon vanilla extract
- 1/4 cup milk of choice
Finish cake batter
While mixing with an electric mixer, pour the ingredients into the dry ingredients and stir until just combined.
Bake the cake
Divide evenly between pans and smooth the tops. Bake at 350°F for 20–25 minutes, or until tops are set and a toothpick comes out clean. Let cool in pans 10 min, then transfer to wire racks.
Make the buttercream frosting
In a large, clean bowl, beat the softened butter with an electric mixer until pale and fluffy (about 4-5 minutes). Add sweetener and beat until combined. Mix in vanilla, then gradually add heavy cream until desired consistency is reached. Frost cooled cake layers.
- 2 cups unsalted butter, softened
- 1 1/2 cups powdered sugar-free sweetener
- 1 1/2 tablespoons vanilla extract
- 1/4 cup heavy cream
Nutrition disclaimer
The nutrition information provided is an estimate and is for informational purposes only. I am a Doctor of Pharmacy (Pharm.D.); however, this content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always consult your physician or other qualified health provider before making any lifestyle changes or beginning a new nutrition program.
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Get My Macros (Free) →Frequently Asked Questions
Can I use whole eggs instead of egg whites?
I've tested this both ways. Whole eggs give you a slightly richer, denser crumb with a yellow tint. For that classic white cake color and a lighter texture, I stick with egg whites. But if you don't mind the color difference, whole eggs work fine. If you want a cake that's designed around a richer, golden crumb, my spice cake is built that way from the start.
What kind of protein powder should I use?
I use unflavored whey protein isolate and I've had the best results with it. It blends smoothly and gives the cake lift without adding flavor. I tried casein and plant-based protein powders early on, and they absorb liquid differently. The cake came out gummy with casein and dense with pea protein. Whey isolate is the only one that works here.
Can I use collagen powder instead of protein powder?
I've tried it, and no. Collagen doesn't create the same structure in baked goods. My cake came out flat and wet. Whey protein isolate is doing real structural work in this recipe, not just adding protein grams. They're not interchangeable.
Can I substitute coconut flour for oat fiber?
You can try, but the results will be different. I've tested coconut flour as a swap and it absorbs a lot more liquid, so you'd need to add extra milk or eggs to compensate. The flavor shifts too. Oat fiber is what gives this cake that light, spongy crumb without adding carbs or coconut taste. If you can get your hands on it, it's worth using.
Can I make this into cupcakes?
I make cupcakes from this batter all the time. Divide evenly into lined cupcake tins and bake at 350 degrees F for about 18-20 minutes, or until the tops are set and a toothpick comes out clean. I usually get 18-20 cupcakes from one batch. They're great for parties because everyone gets their own frosting-to-cake ratio. If you're looking for more cupcake ideas, my Hostess cupcakes are another favorite.
Can I make this dairy-free?
I haven't tested a fully dairy-free version of this exact recipe, but I've had good results swapping butter for coconut oil in other almond flour cakes. The texture shifts a bit (coconut oil makes things firmer once chilled), and you'd need a dairy-free cream for the frosting. I'd use full-fat coconut cream, whipped and sweetened. It won't taste identical to the buttercream, but it works.
What sweetener works best for this recipe?
I've tested this with allulose, monk fruit blends, and erythritol blends. My go-to is a granulated monk fruit and erythritol blend for the cake and a powdered version for the buttercream. Allulose works well too but makes the cake slightly more moist and prone to browning. I'd avoid pure erythritol on its own since it can crystallize and give you a cooling aftertaste.
My daughter's birthday is Friday and I refuse to be assembling a cake at 10pm the night before. If I bake the layers Wednesday and keep them wrapped at room temp, will the texture hold? I've had almond flour cakes go dense after a couple days in the fridge so I'm thinking room temp is the better call.
Room temp wrapped is the right call. Two days is fine with this one. The oat fiber keeps it from going dense the way a plain almond flour cake would. Frost it the day of and you're set.