A gratin is a dish with a crusty top, usually of cheese or breadcrumbs, baked in the oven and then finished by flashing it under a very hot grill, which gives it a gleaming brown topping. Gratins make excellent winter vegetarian dishes. Root vegetables, when combined with onions and cauliflower or broccoli florets, tomatoes, zucchini and corn kernels, make fine gratins. Extra protein can be added in the form of cheese and nuts, within the mix as well as on top.