Heavily grease with butter and line with parchment paper a 10 inch cake pan.
Preheat oven to 300 degrees.
Bring water and sugar to a boil. Remove from heat.
Add chocolates and stir with a whisk until smooth.
Add butter and stir until completely melted (if butter doesn’t melt, put on med heat and stir constantly until it melts).
In a KitchenAid bowl, beat eggs and sugar together for 3 minutes, until light and fluffy (beat for less time if you want a denser cake).
Pour egg foam into folding bowl, then add chocolate mixture and fold together — overmixing is ok.
Pour into cake pan and place on a sheet pan. Place in oven, then add water to the pan.
Bake about 20 to 30 minutes? I’m really not sure — just check until it is set like a custard.
Cool, then freeze in mold with parchment on top.
To unmold, place bottom of pan into hot water for 5 seconds, them invert.
Garnish with whipped cream.