Peel the potatoes, cut them into 3 mm thick slices and soak them in cold water.
Cut in the same way also the zucchini well washed and dried, and the red onions that you have previously peeled and ticked.
Grease a rectangular baking dish with oil and arrange the vegetables, grouping them by type and overlapping them slightly: while you proceed, take care to adjust everything with salt and pepper and sprinkle with a few rosemary needles.
Mix the broth and wine and pour it over the vegetables, then cover with aluminum foil, sprinkle with breadcrumbs and bake for 40 minutes at 180°.
Remove the aluminium foil, sprinkle with grated mild Provolone Valpadana P.D.O. and gratinate for another 15 minutes.