Coarsely chop the walnuts. Cream butter, sugar, vanilla sugar and salt with the whisk of the hand mixer
Peel the banana and mash it with a fork. Add egg and banana to the sugar mixture and mix. Mix flour, baking powder and walnuts and knead
Using a tablespoon, spread about 10 piles of dough on each of two baking trays lined with baking paper. Bring the piles of dough slightly into a round shape. Bake in the preheated oven (electric cooker: 175 °C/ convection oven: 150 °C/ gas: stage 2) for approx. 10 minutes each in succession
Let cookies cool down on the tray
Waiting time approx. 1 hour