First, whisk sugar, vanilla sugar, salt, and soft butter for about 2-3 minutes. Pour condensed milk and mix until you have a solid Mixture. Add in whisked eggs. Mix flour with baking powder and put it in the mixture.
Make cupcake shapes with baking paper. Pour in half the mass. Mix the other half with cocoa and put it on the top. Stir a bit until white and cocoa doughs are mixed.
Bake for about 60 minutes in a 170C oven. You will end up with a soft and delicious cupcake. Enjoy!