Peel and grate the potatoes. Likewise one of the zucchini.

Add flour, egg, pepper, salt and two tablespoons of Parmesan cheese and make a smooth dough that can be rolled out. Chill until ready to use.

Peel the onion and cut into small cubes, coarsely grate the remaining zucchini.

Heat a tablespoon of safflower oil in a pan and fry the frozen mushrooms in it - just don't thaw them beforehand - with half of the onion cubes. Cook while stirring. Season with salt and pepper, then set aside.

Heat the second tablespoon of oil and fry the zucchini grated with the second half of the onion and cook while stirring as well.

Roll out the potato dough on a floured surface. Now first the mushrooms, then two tablespoons of Parmesan and then the courgette on top.

Roll up from the long side and cut approx. 1 cm thick slices.

Heat the clarified butter in a pan and fry the filled potato slices on both sides until golden.