Beat the butter, sugar, salt and vanilla sugar until frothy. Then fold in the eggs one by one. Fold in the banana and sour cream. Mix the flour, baking soda and baking powder in an extra bowl and then sieve over the butter mixture and stir in.
Spread in greased muffin tins or paper liners. Bake at 180 ° C top and bottom heat for 20 minutes. Let the cupcakes cool down.
For the chocolate topping, melt the chocolate over a low heat and let it cool down to lukewarm. Thoroughly stir in the sour cream and immediately spread on the cupecakes.