To Make the Cake:
Get Ready: Preheat your oven to 350°F (175°C).
Combine Dry Ingredients: In a large bowl, whisk together the almond flour, oat fiber, cocoa powder, baking powder, and salt until they are thoroughly blended.
Whip Egg Whites: In a separate, clean bowl, use an electric mixer to beat the egg whites until they form firm, stiff peaks. Set this bowl aside gently.
Mix Wet Ingredients: In another bowl, combine the egg yolks, softened butter, keto sweetener, sour cream, heavy cream, coffee mixture, and vanilla extract. Mix until everything is smooth and well combined.
Fold It In: Gently fold the whipped egg whites into your wet ingredient mixture. Mix just enough until they are combined, being careful not to deflate them too much.
Add Dry to Wet: Now, slowly fold in the dry ingredient mixture from step 2 until everything is just combined. Avoid overmixing to keep the cake tender!
Prepare Pans: Divide the batter evenly between two 8-inch round cake pans. Ensure your pans are lined with parchment paper on the bottom and lightly sprayed or greased on the sides.
Bake Away: Bake for 25-30 minutes, or until a toothpick inserted into the center of the cake comes out clean. Let the cakes cool completely on a wire rack before you even think about frosting them.
To Make the Frosting:
Melt Chocolate: While your cakes are baking and cooling, place the sugar-free chocolate chips in a mixing bowl. Heat the heavy cream in a small pot on the stove just until tiny bubbles begin to form around the edges (do not boil). Pour this hot cream over the chocolate chips and let it sit undisturbed for 5 minutes.
Whisk Ganache: After 5 minutes, whisk the chocolate and cream mixture until it becomes a thick, rich, and smooth ganache. Allow it to cool at room temperature for about 20 minutes.
Finish Frosting: Using a hand mixer, beat the softened mascarpone cheese and keto sweetener into your cooled ganache until everything is well combined and slightly fluffy. Let it continue to sit at room temperature while your cakes finish cooling.
Assemble the Cake: Once your cakes are completely cool, place one cake layer upside down (flat side up) onto your serving plate or cake stand. Pro Tip: For a cleaner serving plate, slide four strips of parchment paper halfway under the edges of the cake.
First Frosting Layer: Spread about one-third of the frosting evenly over the top of the first cake layer using an offset spatula.
Second Cake Layer: Carefully place the second cake layer on top, this time flat side down.
Frost Away: Spread another third of the frosting over the top of the second cake. Use the remaining frosting to generously cover the sides of the cake.
Serve & Enjoy: For an elegant touch, you can create chocolate shavings using a sugar-free chocolate bar and a vegetable peeler to decorate the top. Slice, serve, and savor your incredibly moist and delicious keto chocolate cake!