chocolate mousse cake from @celia_oeg

Boil the milk, sugar, and cocoa in a saucepan then set aside. Mix the eggs with the sugar, oil, milk, and salt. add the flour and baking powder and pour into a 20cm diameter mold. cook for about 15min at 170°c. soak the biscuit with the syrup when it comes out of the oven. leave to cool completely. In a saucepan, mix the egg yolks with the milk, transfer to a low heat and cook until the custard coats the spoon. pour over the chocolate and mix. whip the cold cream and incorporate into the ganache. pour over the cake and refrigerate for at least 1 night.