How to make
Grate the potatoes and zucchini into thin circles.
Season them with salt, a pinch of black pepper and drizzle them with olive oil.
Grease a baking pan with olive oil.
Begin layering the gratin, by starting with the potatoes.
Arrange a row of them, then sprinkle them with sausage and mozzarella pieces, followed by a row of zucchini and again mozzarella and sausage.
From the specified products, I arranged 2 rows with potatoes and two with zucchini.
Sprinkle grated parmesan on top and carefully pour the milk over the side of the baking pan.
Cover the baking pan with a piece of aluminum foil and bake the potato and sausage gratin at 360°F (180°C) for 50 minutes.
Shortly before removing the dish from the oven, remove the foil and bake, until it aquires a golden brown color.
Enjoy!
Note: The zucchini gratin could be made without sausages!