For the pastry: Separate eggs into yolks and whites. Whisk together the egg yolks and sugar until foamy. Mix with the warm milk and flour, then fold in the baking powder and cocoa powder. Whisk the egg whites until stiff and fold in gently. Fill the finished pastry into a greased baking pan and bake for 30 minutes at 180°C.
In the meantime prepare the filling. Heat sugar and water in a pot, stir well until the sugar has completely dissolved. Reduce the temperature and continue cooking until a slightly brownish, thick caramel forms. Add the remaining ingredients (except cream) and simmer until the mixture becomes a thick brown mass. Cool and then mix with Bonny Cream.
Then prepare the topping: Melt butter in a pot, then add the remaining ingredients and allow the mixture to melt for about 5 minutes.
Assemble: Cut the cake horizontally into two halves. Spread most of the filling on the lower half, cover with the top half and spread the rest of the filling. Then, layer the topping evenly on top. Allow to cool.