Coat the inside of a 8” baking pan with butter. Line the bottom with parchment paper and coat it with butter. Make sure the pan is well greased.
Heat oven to 325F (not convection).
Break the chocolate into small pieces and place in a large glass or plastic bowl. Add the butter and melt in the microwave for 2-3 minutes. Stir until smooth.
Heat 1 inch of water in a medium size pot over medium heat.
Place the whole eggs and yolks in a bowl that can sit on top of the pot. Place the pot on top of the pot and whisk the eggs until they reach a temperature of 110F.
Transfer the eggs to a mixer and whisk on high speed until eggs become light and pale, about 5 minutes.
Fold 1/3 of the egg foam into the melted chocolate. Add the rest of the foam and fold gently but thoroughly.
Pour the mixture into the greased baking pan and bake for about 25 – 30 minutes, until cake reaches 170F (you will have to use a thermometer inserted in the middle of the cake).
Remove from the oven and allow to cool in the pan, on a cooling rack, for 20 minutes. Invert the cake onto a cake platter and refrigerate.
In a saucepan, melt the heavy cream, butter and sugar. Mix occasionally and bring to a gentle boil. Remove from the heat. Add the chocolate to the pot and stir until smooth.
Cover the cake with the ganache and keep refrigerated.
The cake can be made well in advance and once cold it can also be kept frozen for a while. Just make sure to freeze it unwrapped until the ganache is hard so that it doesn't smear when you wrap the cake. Then wrap well. The cake can be kept in the freezer for up to 2 months.
