Separate the egg whites from the yolks and beat the whites with most of the sugar until stiff peaks form. Beat the yolks with 1 tbsp sugar separately and mix with the egg whites.
Gently fold in the flour, vanilla, baking powder, and cornstarch.
Bake the layers separately three or four times, or all at once and cut them later. I baked three separate layers.
Beat the Mascarpone, Bonjour cheese, sugar, and milk until smooth. Divide into two parts; mix melted chocolate into one and whipped cream into the other.
Soak the layers with warm milk mixed with cocoa and sugar. Layer cake - cream - cake and press in a cake ring.
Refrigerate overnight, then frost with buttercream and decorate with fondant.