Peel the bananas and mash them with a fork. Wash the strawberries and cut into small pieces. Mix the flour, baking powder and baking soda in a bowl. In a second bowl, beat the eggs, sugar, vanilla sugar, butter, banana puree and buttermilk until frothy. Stir in the flour mixture and strawberry pieces.
Pour the batter into the muffin molds and bake for about 20-25 minutes.