Published On: July 1, 2026Categories: Recipes

This classic Provencal-style gratin layers vibrant summer squash and ripe tomatoes, all held together by a rich, garlic-infused custard and finished with a crunchy, cheesy topping. It’s light yet satisfying, and a perfect side for grilled meats.

Yields: 6-8 servings Prep time: 30 minutes Bake time: 45-55 minutes

Summer Zucchini and Tomato Gratin

Ingredients

  • 2 lbs large zucchini (about 3-4 medium), sliced uniformly 1/4-inch thick

  • 2 lbs ripe Roma or beefsteak tomatoes (about 4-5 medium), sliced uniformly 1/4-inch thick

  • 1 large yellow onion, halved and thinly sliced

  • 3 cloves garlic, minced

  • 2 tablespoons olive oil, divided, plus extra for greasing

  • 1 tablespoon fresh thyme leaves (or 1 tsp dried)

  • 1 tablespoon fresh oregano, chopped (or 1 tsp dried)

  • 1 cup heavy cream

  • 1/2 cup whole milk

  • 3 large eggs

  • 1/2 teaspoon ground nutmeg (optional)

  • 1/2 cup Gruyère cheese, shredded (or Swiss/Fontina)

  • 1/2 cup Parmesan cheese, finely grated

  • 1/2 cup panko breadcrumbs

  • 1 teaspoon Kosher salt, plus extra for sweating zucchini

  • 1/2 teaspoon freshly cracked black pepper

Instructions

1. Prepare the Vegetables

  • Place the sliced zucchini in a large colander in the sink. Sprinkle generously with salt and toss. Let sit for 15-20 minutes to draw out excess moisture. Rinse and pat dry very well with paper towels.

  • In a large skillet, heat 1 tablespoon of olive oil over medium heat. Add the sliced onion and cook, stirring occasionally, until soft and translucent (about 8 minutes). Stir in the minced garlic and cook for 1 minute more until fragrant. Remove from heat.

2. Assemble the Gratin

  • Preheat your oven to 375°F (190°C). Grease a 9×13 inch baking dish (or a large, shallow ceramic gratin dish) with olive oil.

  • Spread the sautéed onion and garlic mixture evenly across the bottom of the dish.

  • Arrange the zucchini and tomato slices by tightly overlapping them in alternating, shingled rows (Zucchini-Tomato-Zucchini-Tomato) across the prepared dish, starting at one end and working to the other.

3. Make the Custard

  • In a medium bowl, whisk together the heavy cream, milk, eggs, fresh thyme, oregano, nutmeg (if using), 1 teaspoon salt, and 1/2 teaspoon black pepper.

  • Carefully pour the custard mixture evenly over the entire vegetable arrangement.

4. Prepare the Topping

  • In a small bowl, combine the shredded Gruyère cheese, grated Parmesan cheese, and panko breadcrumbs. Add the remaining 1 tablespoon of olive oil and mix until the topping is uniformly moistened and crumbly.

  • Sprinkle the topping evenly over the entire surface of the gratin.

5. Bake to Golden Perfection

  • Bake the gratin for 45 to 55 minutes, or until the vegetables are tender, the custard is set, and the top is deeply golden and bubbling. Tip: If the top browns too quickly, cover it loosely with foil for the remaining bake time.

  • Remove from the oven and allow it to rest for at least 15 minutes before serving. This rest allows the gratin to firm up, making it easier to slice neatly.

6. Serve

  • Garnish with a sprinkle of fresh chopped basil or parsley right before serving. Enjoy warm or at room temperature.