Equipment list: Large non-stick oven safe skillet, 12-inch or better. Cast iron also works. Serving platter that is larger than skillet. Cook's notes: When flipping the tart over onto your serving platter, some of the onions and potatoes may stick to your pan. Just have a spatula ready and carefully scrape them off the pan and place them back where they belong on the tart. If you really like cheese, this tart can be made with any favorite cheeses you have on hand and I've made it with double the mozzarella and have used cheddar in place of the Parmesan. Experiment to your own liking.