Preheat the oven to 350ºF and grease an 8 inch round metal baking pan. Line the bottom with parchment and grease the parchment.
In a large bowl, whisk together the almond flour, sweetener, protein powder, baking powder, and salt. Whisk in the eggs, butter, water, and vanilla extract until well combined and smooth.
Transfer about one-third of the batter to another bowl and whisk in the cocoa powder and a few more tablespoons of water or coffee. The chocolate batter should be the same consistency as the vanilla batter.
Drop a spoonful of vanilla batter in the center of the prepared pan. Then drop a spoonful of chocolate batter in the very center of the vanilla batter.
Tap the pan gently on the counter to help the batter spread toward the edges. Repeat with alternating spoonfuls of batter until both batters are used up.
Bake 25 to 30 minutes, until the top of the cake is just firm to the touch. Remove and let cool completely, then run a sharp knife around the edges and flip out onto a wire rack.
Frosting
Prepare the frosting as directed in the recipe. Spread over the top and sides of the cake. Sprinkle with keto sprinkles, if desired.
Notes
Storage Information: Store this cake in the fridge for up to a week. The cake and frosting taste best at room temperature so let it sit out for a bit before serving. For leftovers, be sure to cover any of the exposed sides with plastic wrap to keep it from drying out. You can also freeze the cake for several months. Sweetener Options:You can make the cake with other granular sweeteners, but do be aware that allulose tends to make things brown too quickly. So the vanilla portion may look darker on the outside. It will still be light colored when you slice into the cake.The frosting requires a powdered sweetener for structure.