For the cake, preheat the oven to 325F and grease 2 8-inch round cake pans. Line cake pans with parchment paper and grease the parchement.
In a large bowl, whisk together almond flour, cocoa powder, protein powder, granulated erythritol, instant coffee, baking powder, baking soda, xanthan gum and salt.
In another large bowl, beat Greek yogurt and butter together until combined. Beat in eggs and stevia extract. Beat in almond flour mixture in two additions, alternating with almond milk, and scraping down beaters and sides of bowl as needed.
Divide batter between prepared pans and bake 30 to 35 minutes or until cakes are set and a tester inserted in center comes out clean. Let cool in pans 10 minutes, and then flip out onto wire racks to cool completely.
Once cool, use a large serrated knife to cut each layer in half horizontally to create 4 layers total.
For the frosting, in a small saucepan over low heat, melt chocolate and stir until smooth. Set aside.
In large bowl, beat sour cream and powdered erythritol until smooth. Beat in cocoa powder, then vanilla extract and stevia extract.
Sprinkle xanthan gum over mixture and beat in until frosting thickens slightly. Stir in melted chocolate, scraping down sides of bowl, until well combined.
Place one layer of cake on serving platter and top with 1/2 to 3/4 cup frosting, using knife or offset spatula to spread evenly. Repeat with remaining layers and frosting. For final layer, top with any remaining frosting and spread down and over sides of cake, smoothing with knife or offset spatula. If desired, use back of small spoon to create swirled effect on top of cake.
Chill cake in refrigerator for at least one hour. Any leftover cake should be wrapped in plastic and kept in refrigerator.
Each serving has a total of 10g of carbs and 5g of fiber. Total NET CARBS = 5g.