Preheat oven to 400 degrees. Generously butter a cake pan and line with parchment paper. Prepare the ganache by putting all of the chocolate into a small saucepan on medium heat. Stir in whipped cream and butter. Stir until fully incorporated, 6-10 minutes. Add coffee to ganache and remove from heat. In a separate bowl, whip the eggs, sugar and flour until nearly doubled in size, about 6 minutes. Add the ganache to the eggs, whipping at a medium speed. Pour the ganache into the prepared pan. Bake for 15-20 minutes, until the top and edges are set, and a toothpick can come out clean. Refrigerate for at least 3 hours until properly chilled. Sift the cocoa powder on top.