Give the butter a short run in the microwave to soften it - or take the butter out of the fridge well in advance. The butter should be completely soft but not melted.
Find a bowl and a hand mixer.
Put sugar, eggs, and vanilla sugar in the bowl and whisk it all until airy.
Find a new bowl.
Put flour and baking powder in the new bowl.
Find another new, small bowl and mash the bananas in it with a fork.
Find a cutting board and chop the chocolate into coarse pieces.
Set the hand mixer aside and instead find a spoon or a spatula.
Gently fold the mixture of flour and baking powder into the bowl with the egg mixture.
Then add the soft butter and gently fold it into the mixture as well.
Finally, add the chopped chocolate and mashed bananas to the mixture and fold - again gently. Make sure all the flour is well mixed in and that the batter is smooth and uniform.
Find 14 muffin cups.
Distribute the batter in each cup using a piping bag or a spoon (we just used a tablespoon).
Preheat the oven to 180 degrees Celsius (356 degrees Fahrenheit) (fan-assisted).
Place your banana muffins in the now hot oven and bake them for approximately 17 minutes.
Test if they are done by poking them with a paring knife - there should be no batter sticking to it.
Take the finished muffins out and let them cool on a rack.