This French-style buttercream is rich and dense and melts very easily on the tip of the tongue, so it suits a cake like a Dobos torte that sandwiches it between all those thin cake layers.
Melt the semisweet and bittersweet chocolate together in a metal or glass bowl placed over a pot of barely simmering water, stirring until melted. Set aside.
Place the egg yolks in a large bowl and whip with ¼ cup (60 mL) of the sugar until they are pale and have doubled in volume, about 3 minutes.
Bring the remaining ¼ cup (60 mL) of sugar, the water