First beat the eggs until they're foamy while stirring in the sugar. Now add the dark chocolate and melted butter, mixing everything together. Next, work in the flour, cocoa, coffee powder, and baking powder. Stir all the ingredients into a creamy mixture.
Repeat the first step so that you have two round cake pans filled with the chocolate batter mixture. Bake them at 320°F with the top and bottom heat on for 35 minutes.
Cut the baked cakes horizontally into thin slices. The top layer on each cake is no longer needed, so you can eat that already. ;-)
Mix the dark chocolate with hot cream. Leave the chocolatey cream mix to cool to room temperature and then carefully fold in the whipped cream.
Take a slice of cake, spread cream onto it, and then place another slice on top. Once all of the slices have been stacked, cover the outside of the cake tower with the rest of the mousse.
Next pour the melted dark chocolate on top. To finish, mix the cocoa with the coffee powder and sprinkle it along the side of the cake.