Protein Cake (Moist & Fluffy!) with 2-Ingredient Fudge Frosting

protein cake with chocolate fudge frosting topped with berries

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This moist and fluffy protein cake is soft, tender, and actually tastes like cake. It’s made with oat flour, whey protein, and a small blend of olive oil and butter for the perfect crumb. Lightly sweetened with maple syrup and finished with a rich two-ingredient fudge frosting, it’s a better-for-you dessert that still feels indulgent.

Prep Time15

Cook Time25

Total Time40

Course: Dessert

Keyword: Oat flour, Protein

Servings:

Calories: 280kcal

Author: Crystal Yentzen

Equipment

Ingredients

For the cake

1 and ½ cups oat flour*
½ cup vanilla whey protein powder*
¼ cup cornstarch
1 tablespoon baking powder
½ teaspoon salt
⅔ cup maple syrup or liquid sweetener of choice
2 large eggs
3 tablespoons olive oil or neutral oil
2 tablespoons butter melted
3 tablespoons milk of choice
2 teaspoons vanilla extract

For the frosting

½ cup chocolate chips of choice
2 tablespoons peanut butter* see notes

Instructions

For the Cake

Preheat the oven to 335ºF. Lightly spray an 9-inch round cake pan with non-stick spray, line the bottom with a parchment round, then spray the parchment. This ensures your cake doesn't stick. (You can also just spray the pan if you prefer.)
In a large bowl, whisk together the oat flour, protein powder, cornstarch, baking powder, and salt.
In a separate bowl, whisk together the maple syrup, eggs, olive oil, melted butter, milk, and vanilla until smooth.
Pour the wet ingredients into the dry ingredients and stir until just combined. Let the batter rest for 4–5 minutes to allow the oat flour to hydrate, then give it a quick stir.
Pour the batter into the prepared cake pan. Bake for 22–25 minutes or until a toothpick inserted into the center comes out clean or with a few moist crumbs. Let the cake cool for 10 minutes in the pan before transferring it to a wire rack to cool completely.

For the frosting

When the cake is cool, prepare the fudge frosting.
Melt the chocolate chips and peanut butter together in the microwave in 20-second intervals, stirring until smooth.
Spread the frosting over the cooled cake (the sides can be left unfrosted). It’s delicious right away, or let it sit for a few hours to set into a fudge-like layer.
Slice, serve, and enjoy! Please leave a rating if you try this recipe.

Notes

Oat Flour- Oat flour gives this protein cake a soft, tender crumb and adds more whole-grain nutrition than all-purpose flour. If you’re making your own, use finely blended oats for the best texture. I share more tips and troubleshooting in my oat flour guide if you’re new to baking with it.

Vanilla Whey Protein Powder- I used Levels Vanilla Bean Whey Protein. Feel free to use any vanilla whey protein you enjoy. I can't guarantee the same results using a plant-based protein powder because it tends to be more absorbent than whey. If you decide to use a plant-based protein, add a splash (about 2 tablespoons) of milk of your choice to the batter.

Peanut Butter- For best results, use processed creamy peanut butter such as Jif or Skippy. We do not recommend oily or natural style peanut butter because the topping will separate.

Storage- Store leftover protein cake in an airtight container at room temperature for 2 days or in the refrigerator for up to 5 days. For longer storage, slice and wrap individual pieces tightly and freeze for up to 2 months. Thaw overnight in the refrigerator or at room temperature before serving.

Nutrition