Line a baking sheet or mold / jar with biscuits, which you sprinkle with rum (if you like more soggy biscuits, you can also sprinkle them with milk).
Prepare the cream no. 1. Heat 2 cups of milk on the stove, add a little rum to it. In another bowl, mix crystal sugar, vanilla sugar and corn starch, pour in the remaining milk and mix to obtain a smooth mixture. When the milk starts to boil, add the smooth mixture and cook for about 2 minutes. Then add the butter and pour the whole mixture while still hot onto the biscuits.
While the cream no. 1 cools on the biscuits, you will prepare the cream no. 2. Put the whipping cream on a low heat, add the smaller pieces of chocolate to it and cook until the chocolate melts. Remove from heat, let cool slightly and pour over cream no. 1.
The black and white cake layered in this way must be left aside and cool. Put it in the fridge for at least 2 hours and then you can cut it into slices and serve.