For the Moist Chocolate Cake:
Preheat your oven to 350°F (175°C). Line two 9-inch round cake pans with parchment paper and lightly grease the sides. This ensures your beautiful cakes won't stick!
In a large mixing bowl, whisk together the almond flour, oat fiber, cocoa powder, baking powder, and a pinch of salt until everything is perfectly combined. Set this aside.
In a separate, clean bowl, use a hand mixer to beat the egg whites until they form stiff, fluffy peaks. Gently set these aside – they'll give your cake that wonderful light texture!
In another bowl, mix the egg yolks, softened butter, 1 ½ cups of your chosen powdered sweetener, sour cream, ½ cup heavy cream, instant coffee granules, and vanilla extract. Beat until smooth and well blended.
Carefully fold the whipped egg whites into the wet mixture until just combined. Then, gradually fold in your dry ingredients, mixing gently just until no streaks remain. Remember, don't overmix to keep the cake light and airy!
Divide the batter evenly between your two prepared cake pans. Bake for 25-30 minutes, or until a toothpick inserted into the center comes out clean. Let the cakes cool completely on a wire rack before frosting – patience is key for a perfect, non-crumbling cake!
For the Rich Ganache Frosting:
While the cakes are baking, place the sugar-free chocolate chips in a heatproof bowl. In a small saucepan, heat 1 ⅓ cups heavy cream over medium heat until small bubbles just start to form around the edges.
Pour the hot cream over the chocolate chips and let it sit undisturbed for 5 minutes. Then, whisk the mixture gently until it transforms into a smooth, thick, and glossy ganache. Allow it to cool at room temperature for about 20 minutes.
Using a hand mixer, beat the softened mascarpone cheese and the remaining 2 tablespoons of powdered sweetener into the cooled ganache until everything is light and creamy. Keep this at room temperature until your cakes are fully cooled.
Once the cakes are completely cool, place one cake layer (flat side up) onto your serving plate or cake stand. Spread about one-third of the frosting evenly over the top. Carefully place the second cake layer on top (flat side down this time). Spread another one-third of the frosting over the top. Finally, use the remaining frosting to cover the sides of the cake. For an extra special touch, garnish with some sugar-free chocolate shavings!