This is a classic Provençal dish of thinly sliced vegetables that are arranged in rows and drizzled with olive oil, then cooked until almost caramelized.Plus: More Vegetable Recipes and Tips
Preheat the oven to 400°. Grease a 12-by-10-inch shallow baking dish with olive oil. Arrange one-third of the eggplant slices in an overlapping row across the dish. Season with salt and pepper. Similarly, make a row of zucchini, followed by a row of tomatoes. Repeat until all the vegetables are used.
Drizzle the vegetables with the olive oil and sprinkle with the rosemary. Bake for about 40 minutes, or until the vegetables are very tender and starting to brown around the edges.
The gratin can be baked a few hours ahead of time and quickly reheated just before serving.