A tian is a type of gratin, typically vegetables baked in an earthenware dish. (The word “tian” also refers to the earthenware dish itself.) This classic Provençal version is made with alternating rows of sliced zucchini, eggplant, and tomato. The flavors meld as the vegetables cook together, somewhat like ratatouille. Seasoned simply with thyme, garlic, and good fruity olive oil, the dish is best served at room temperature. Lulu insists it tastes even better made a day in advance.