Start by preheating the oven to 200 degrees Celsius (392 degrees Fahrenheit).

Put sugar, wheat flour, baking powder, vanilla sugar, cocoa powder, and salt in a bowl and mix it with a spoon.

Crack the egg into another bowl and whisk it together with milk and oil for about a minute.

Pour it into the bowl with the dry ingredients and mix it together.

Add the chopped chocolate and stir it around.

Fill muffin cups halfway with batter, so they have room to rise.

Place your cupcakes in the preheated oven and let them bake for about fifteen minutes. The baking time depends on your oven, but you can test if they are done by sticking a knitting needle or the tip of a paring knife into them. They are done when no batter sticks to it.

Mix butter and powdered sugar together in a bowl.

Add the water and mix everything together until it has a creamy consistency. You can always add a bit more powdered sugar if you think it's necessary.

Add a few drops of the chosen food coloring and mix it well into the frosting. Surprisingly, my daughter chose green, even though her favorite color is pink!

Put the frosting in the refrigerator for about an hour.

Put the finished frosting in a piping bag with a nozzle and pipe it onto the cakes.

Finish by decorating with some sprinkles and balls, or whatever you like, and serve!