Zucchini-Fennel Gratin

Preheat the oven to CONVECTION/BAKE 425°F. Place the oil, zucchini, fennel, onion, salt, and pepper in a 2½-quart casserole dish and toss to combine. Bake until the vegetables are just tender and begin to brown, about 25 minutes.

Whisk together the cream and nutmeg in a small bowl and pour over the vegetables. Sprinkle the Gruyère evenly over the top and bake until the cream begins to bubble, about 15 minutes. In another small bowl, combine the panko and the Parmigiano-Reggiano. Remove the baking dish from the oven and sprinkle the panko mixture evenly over the top. Bake until the crumbs are golden brown, about 10 minutes. Remove from the oven and let stand for about 15 minutes before serving.

Sweet Potato Gratin

Whisk together the cream, 1 teaspoon ground cinnamon, and ¼ teaspoon ground cloves in a large bowl. Substitute 2 pounds peeled, very thinly sliced sweet potatoes for the zucchini, fennel, and onion. Add the sweet potatoes to the cream and toss to coat. Turn the sweet potato mixture into a small baking dish (omit the Gruyère). Cover the baking dish tightly with foil and bake until the sweet potatoes are tender, about 30 minutes. In another small bowl, stir together the panko and 2 tablespoons melted unsalted butter, then sprinkle it evenly over the potatoes and bake until the potatoes are golden brown, about 20 minutes. Remove from the oven and let stand for about 15 minutes before serving.

Crispy Broccoli Gratin

Substitute 1 pound broccoli florets and stems and 1 minced garlic clove for the zucchini and fennel. Substitute ½ teaspoon chopped fresh thyme for the nutmeg.