Clean, wash, sort and drain the spinach. Peel garlic and onion, dice finely. Sauté in hot olive oil. Add the spinach, cover and let it collapse on top. Season with salt, pepper and vinegar, drain.
Stir the croquette powder into 375 millilitres of cold water, allow to swell for ten minutes. Knead in the Parmesan cheese. Roll out the potato dough between two layers of foil to a plate (20 by 30 centimetres).
Spread drained spinach on top. Roll it up from the narrow side with the help of the foil and cut it into eight slices. Heat clarified butter in a coated pan. Fry the vegetable slices for two to three minutes on each side.
Tomato sauce tastes good with it. Serve sprinkled with sliced parmesan and basil leaves and garnished.