Ingredients

Equipment Needed

• •9x13-inch baking dish or oval gratin dish
• •Sharp knife or mandoline
• •Large skillet
• •Aluminum foil

Instructions

1. 1

   Salt the eggplant

   Lay eggplant slices on a clean kitchen towel in a single layer. Sprinkle both sides lightly with sea salt and let them rest for twenty minutes. The salt draws out moisture and any bitterness, and the slices will become supple rather than spongy. Pat them dry before proceeding.

   Young, freshly picked eggplant from a farmer you trust rarely needs salting. Taste a raw slice. If it is sweet and mild, skip this step.
2. 2

   Soften the onions

   Warm three tablespoons of olive oil in a skillet over medium-low heat. Add the sliced onion and a pinch of salt. Cook slowly, stirring occasionally, until the onion is soft and translucent, about twelve minutes. You want sweetness, not color. Add the garlic in the final minute, just until fragrant. Set aside.

3. 3

   Prepare the baking dish

   Preheat your oven to 375°F. Brush a 9x13-inch baking dish (or a round gratin dish of similar volume) with olive oil. Scatter half the softened onions across the bottom. This creates a sweet, aromatic foundation for the vegetables to rest upon.

4. 4

   Layer the vegetables

   Arrange the vegetable slices in overlapping rows, alternating zucchini, yellow squash, eggplant, and tomato. Stand them at a slight angle so you can see the colors. The pattern does not need to be perfect. Let it look like what it is: a garden captured in a dish. Scatter the remaining onions and half the thyme between layers.

5. 5

   Season and oil

   Drizzle three tablespoons of olive oil evenly over the vegetables. Sprinkle with the sea salt, pepper, and remaining thyme. The oil will pool between the slices and baste them as they cook. Use your hands to gently press the vegetables down so they nestle together.

   Good olive oil matters here. It should taste green and peppery on its own. You are not just cooking with it; you are seasoning with it.
6. 6

   Cover and bake

   Cover the dish tightly with foil and bake for forty minutes. The vegetables will steam in their own juices, becoming tender and releasing their liquid. The kitchen will smell of summer.

7. 7

   Add the topping

   Remove the foil. Toss the breadcrumbs with the cheese and remaining olive oil. Scatter this mixture over the vegetables and dot with butter. Return to the oven, uncovered, for twenty to twenty-five minutes until the top is golden and crisp and the vegetables are completely tender when pierced with a knife.

8. 8

   Rest and finish

   Let the gratin rest for ten minutes before serving. Scatter the torn basil over the top. The dish will hold together better with a brief rest, and the flavors will have a moment to settle into one another. Serve warm or at room temperature.

   This gratin is even better the next day, when the flavors have deepened overnight. Reheat gently or serve at room temperature.

Chef Tips

• •At the market, look for summer squash that feels firm with glossy, unblemished skin. Small to medium squash have fewer seeds and more flavor than overgrown ones.
• •Tomatoes should smell like tomatoes. If they have no perfume at the stem end, they will have no flavor in the dish. Wait for better ones or find a different farmer.
• •Slice your vegetables the same thickness so they cook evenly. A mandoline helps if you have one, but a sharp knife and patience work just as well.
• •This gratin welcomes variation. Add a layer of sliced fennel, substitute fresh oregano for thyme, or scatter olives between the layers. Let the market guide you.
• •If you can find young garlic with green stems, use it. The flavor is milder and sweeter than cured garlic, and it melts into the dish.

Advance Preparation

• •The gratin can be assembled completely, covered, and refrigerated for up to eight hours before baking. Add ten minutes to the covered baking time if starting cold.
• •Baked gratin keeps refrigerated for three days. Reheat at 350°F for fifteen minutes, or serve at room temperature.
• •This dish travels well to potlucks. Transport it in the baking dish, covered with foil. It holds its warmth for about an hour.

Frequently Asked Questions

Nutrition Information

1 serving (about 240g)