Peel the potatoes, cut them into cubes and cook in lightly salted water for about ten minutes. Drain and put in a bowl.

Grate the zucchini, carrot and cabbage with a grater with large holes. Mash the potatoes with a fork, add all the vegetables, salt and egg, mix well.

Take a portion of the mixture, about a generous tablespoon, make a large meatball, then flatten it to form a medallion or use a pastry cutter to give it the typical shape. Oil a pan and cook the medallions on both sides, alternatively the oven at 180° is fine for 15-20 minutes.

Stuff the hamburger bun with the vegetable medallions and slices of sweet Provolone Valpadana DOP, pair them up and sauté them in a pan with the lid closed for a few minutes or in the oven at 160° for 5-6 minutes.