Separate the egg whites from the yolks and beat the egg yolks with 2/5 cup (100 g) sugar. Add the lemon peel and stir gently with the remaining sugar that you've beaten separately with the whites. Then mix in the cocoa, nuts and flour.
Pour the mixture into a form with paper baking and put it to bake in a moderate oven until tender (check at the end with a toothpick).
Cut the cooled layer into 3 separate ones (or more if possible) and syrup each with sugar syrup with a spoon of rum in it.
For the cream, put the milk with a portion of the sugar to boil. Separately, beat the eggs with the remaining sugar. Add them to the flour and 1-2 vanilla packets. In a thin stream and while beating nonstop, add the egg mixture to the milk cream and stir until thickened.
Let it cool a little, then mix it with the butter. Stick the soaked cake layers with cream and cover the top with cream, too. Garnish with chopped walnuts or grated chocolate.