Preheat oven to 350 F. Grease two 6-inch round cake pans with butter. Set aside.
In a bowl combine the dry ingredients - coconut flour, almond flour, baking soda, baking powder, xantan gum. salt and cocoa powder.
Combine almond milk with vinegar (lemon juice).
In a separate bowl beat the eggs with powdered erythritol for 4-5 minutes on medium-high speed. Add in the vanilla extract, coffee extract, coconut oil.
Add in 1/2 of the dry ingredients to the egg and sweetened mixture. Mix to combine. Add 1/2 of the milk and mix to combine.
Repeat by adding the remaining liquid and dry ingredient and mix until just combined.
Divde batter between the two pans. Smooth out the tops. Bake for 25-30 minutes, until toothpick inserted comes out clean.
Let the cakes cook inside the pans for 10 minutes and then transfer to wire rack to cool down completely.
Using a serrated knife cut the cakes in half horizontally.
Melt the chocolate and let it cool for 5 minutes.
In a bowl mix together the mascarpone, cocoa powder and sweetener, using a spatula.
Mixing on medium speed with an electric mixer, slowly add in the heavy cream. Mix just until the Cream has been incorporated and thickened. Over mixing or mixing on high speed may result into the mascarpone separating and releasing liquid.
Slowly, add in the melted chocolate, mixing on slow speed until combined.
Assemble the cake by layering cake layers and filling, leaving the top without any filling.
Place chocolate in a bowl. Heat the heavy cream to a boil. Pour over the chocolate. Mix to combine.
Pour ganache over the top of the cake and smooth with a spatula. Top with berries.