Preheat oven to 325 degrees. Choose an 8” cake pan or your favorite silicone mold. Baking time will be less if you choose smaller pans for individual desserts. You will also need a cardboard cake round.
Over a double boiler melt together chocolate and butter. In a separate bowl, whip egg whites into a stiff peak; set aside. Using a stand or handheld mixer, whip egg yolks and sugar until they have reached full volume. Turn mixer on low and slowly add melted chocolate to egg yolk and sugar mixture. Once combined, fold in egg whites. Egg whites will appear slightly lumpy, but will ensure that your cake rises.
Pour cake mixture into pan. Set on baking sheet. Put baking sheet onto oven rack. Pour ¼” water onto baking sheet, being careful not to get water on the cake; the water will help the cake rise.
If using a cake pan, spray with cooking spray, line bottom with parchment paper, then spray again. Silicone molds do not require cooking spray. Bake approx. 40 min or until there is a uniform jiggle to the cake. Let cool slowly on counter or in the oven with the door ajar and the oven turned off. Once cool, chill in the refrigerator until fully set.
To remove, loosen the cake and flip onto cake plate or stand.
For chocolate ganache, slowly melt chocolate, add cream and stir until combined.
Coat cake with ganache. Chill until set. Slice and serve.