Provençal Vegetable Gratin (Tian) | Saveur

Ingredients

• 6 tbsp. extra-virgin olive oil, plus more
• 2 large white or yellow onions, thinly sliced
• Kosher salt and freshly ground black pepper
• 2 tsp. chopped thyme
• 1 ⁄ 4 tsp. crushed chile flakes
• 6 cloves garlic, minced
• 1 lb. medium zucchini, cut into 1/4-inch-thick slices
• 1 1 ⁄ 2 lb. small, firm eggplant, cut into 1/4-inch-thick slices
• 1 1 ⁄ 2 lb. ripe tomatoes, cored and cut into 1/4-inch-thick slices
• Torn basil leaves, for garnish