The Cheesiest Zucchini Gratin in the World

The cheesiest zucchini gratin in the world is made with salted zucchini, a silky cream sauce, nutty Gruyere, Parmesan, and a crisp breadcrumb topping. Bake it at 375°F (190°C) for 35–45 minutes, then rest it for 10 minutes so the bubbling sauce settles into every tender slice.

This is the zucchini side dish for anyone who thinks vegetables should arrive at the table cloaked in cheese. The squash becomes soft but flavorful, while onion, garlic, thyme, and a whisper of nutmeg give the sauce savory depth beneath its golden, crunchy crust.

Why You’ll Love This Recipe

This zucchini gratin has everything a great comfort-food side dish should offer: creamy sauce, mellow vegetables, a savory cheese pull, and a browned topping that crackles lightly under your fork. Gruyere brings a nutty, buttery flavor, while Parmesan adds salty intensity and helps the crumbs turn beautifully golden.

The recipe is also carefully designed to protect the sauce from the watery texture that can affect baked zucchini. A short salting step draws out moisture before the squash enters the dish, and the shallow baking arrangement gives heat plenty of room to reach every layer.

Serve it beside roast chicken, grilled steak, baked fish, or a simple green salad. If you enjoy creative ways to cook this vegetable, our crispy air fryer zucchini is another excellent option for a lighter side.

Ingredients You’ll Need

Choose firm, glossy zucchini or summer squash and slice it into rounds about 1/4 inch thick. Consistent slices matter because they soften at the same rate, giving you a gratin that is tender throughout rather than a mixture of crunchy and collapsed pieces.

• Zucchini: Two pounds provides a generous vegetable base for a 2-quart shallow dish.
• Aromatics: Yellow onion, garlic, and thyme give the cream sauce its savory foundation.
• Dairy: Whole milk and heavy cream create a rich but pourable sauce.
• Cheese: Gruyere melts smoothly, while divided Parmesan flavors the sauce and the topping.
• Crunch: Panko or fresh breadcrumbs mixed with olive oil or melted butter finish the dish with a crisp crust.

Nutmeg is optional, but a small amount adds classic cream-sauce warmth without making the gratin taste sweet or heavily spiced. Fresh thyme has the brightest flavor, although dried thyme works well when that is what you have available.

For another easy vegetable-centered dinner idea, pair this gratin with a simple sheet pan dinner and let the oven handle the main course and side dishes together.

How to Make It Step-by-Step

Step 1: Heat the oven to 375°F (190°C), then butter a 2-quart gratin dish or another shallow baking dish. Coating the dish helps the edges release easily and gives the sauce a buttery flavor as it bubbles around the squash.

Step 2: Put the sliced zucchini in a large bowl and toss it with 1 teaspoon of kosher salt. Let it stand for 20–30 minutes, then pat every slice very dry with paper towels; this is the most important defense against a watery gratin.

Step 3: Melt 2 tablespoons of unsalted butter in a saucepan over medium heat. Add the finely chopped onion and cook for about 5 minutes, stirring occasionally, until soft but not deeply browned.

Step 4: Add the minced garlic and thyme, cooking for another 30 seconds until fragrant. Stir in the flour and cook for about 1 minute so it blends into the butter and loses its raw flour taste.

Step 5: Gradually whisk in the whole milk and heavy cream, adding them slowly to keep the sauce smooth. Simmer for 3–5 minutes, stirring frequently, until lightly thickened, then season with black pepper and optional grated nutmeg.

Step 6: Remove the saucepan from the heat and stir in the Gruyere along with about 1/4 cup of the Parmesan. The residual heat should melt the cheese into a glossy sauce without requiring a hard boil.

Step 7: Arrange half of the dried zucchini rounds in the prepared dish, keeping the layer fairly even rather than piling the slices too high. Spoon half of the cheese sauce over the squash, then repeat with the remaining zucchini and sauce.

Step 8: Combine the panko or fresh breadcrumbs with the remaining Parmesan and 1 tablespoon of olive oil or melted butter. Scatter the mixture over the entire surface so every serving has both creamy filling and crisp topping.

Step 9: Bake for approximately 35–45 minutes, watching for tender zucchini, bubbling sauce, and a golden crust. If you prefer a darker finish, broil the gratin for 1–3 minutes, watching constantly because breadcrumbs can brown quickly.

Step 10: Let the gratin rest for 10 minutes before serving. This brief pause allows the sauce to thicken slightly, keeps the layers intact, and prevents the first spoonful from running across the plate.

Chef’s Tips for the Creamiest Gratin

The first rule is simple: do not skip the salting and drying step. Zucchini contains a great deal of water, and baking draws that moisture out; removing some before layering gives the cream sauce a much better chance of staying thick and luxurious.

Use a shallow dish rather than a deep casserole. A wide, low arrangement prevents the slices from being stacked too thickly, encourages even cooking, and provides more surface area for the Parmesan breadcrumb crust to brown.

Whisk the milk and cream into the flour mixture gradually. This creates a smooth base, while a gentle simmer thickens the sauce without scorching it. Once the cheese goes in, remove the pan from the heat and stir until melted.

Keep the seasoning balanced because Gruyere and Parmesan already contribute salt. Taste the sauce before adding any extra salt, especially if your butter, cheese, or breadcrumbs are seasoned.

For a complete comfort-food menu, serve this gratin beside a creamy chicken bake. The crisp topping and fresh thyme cut through the richness of a hearty main course.

What to Serve with Zucchini Gratin

This dish is rich enough to anchor a vegetarian dinner when served with a crisp salad, but it is especially wonderful as a side. The creamy zucchini pairs naturally with roast chicken, pork tenderloin, baked salmon, and simply seasoned steak.

For a lighter plate, add a bright vegetable with a little snap, such as tender roasted asparagus. A lemon-dressed salad or sliced tomatoes also brings acidity that keeps the meal feeling fresh.

If you are serving the gratin at a relaxed family supper, a bowl of soup makes the table especially welcoming. Try it with slow-cooked cabbage soup for a cozy menu with contrasting textures and flavors.

Storage and Reheating

Let leftovers cool, then cover and refrigerate them promptly. Store the gratin in the refrigerator and enjoy it reheated until hot throughout; the breadcrumb topping may soften slightly, but the cheesy center remains delicious.

For the best crust, reheat individual portions or the baking dish in a 375°F oven until warmed through, then use the broiler briefly if needed. Avoid broiling unattended, and remember that the dish will be hot and bubbling as it comes from the oven.

If you are planning ahead, prepare the sauce and dry the zucchini close to cooking time, then assemble the layers just before baking. This keeps the breadcrumbs crisp and limits the time the salted squash has to release additional moisture.

The Cheesiest Zucchini Gratin in the World

Thinly sliced zucchini is layered with a creamy Gruyere cheese sauce and finished with Parmesan breadcrumbs. Salting and drying the squash first keeps the gratin rich and bubbling instead of watery.

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Prep Time 20 minutes mins

Cook Time 35 minutes mins

Total Time 1 minute min

Servings: 4 servings

Ingredients Method Notes

Ingredients

  

Zucchini and Sauce

• 2 pounds zucchini or summer squash, sliced into approximately 1/4-inch rounds
• 1 teaspoon kosher salt, plus more for seasoning
• 2 tablespoons unsalted butter
• 1 small yellow onion, finely chopped
• 2 garlic cloves, minced
• 2 tablespoons all-purpose flour
• 1 cup whole milk
• 1/2 cup heavy cream
• 1/2 teaspoon freshly ground black pepper
• 1/4 teaspoon grated nutmeg, optional

Cheese and Topping

• 1 cup Gruyere cheese, grated
• 1/2 cup finely grated Parmesan cheese, divided
• 1/2 cup panko or fresh breadcrumbs
• 1 tablespoon olive oil or melted butter
• 1 tablespoon fresh or 1 teaspoon dried fresh thyme, chopped, or dried thyme

Method

 

Step-by-Step

1. Heat the oven to 375°F (190°C) and butter a 2-quart gratin dish or shallow baking dish.
2. Toss the sliced zucchini with 1 teaspoon kosher salt and let it stand for 20–30 minutes. Pat the rounds thoroughly dry with paper towels.
3. Melt the butter in a saucepan over medium heat. Cook the onion until soft, about 5 minutes, then add the garlic and thyme and cook for another 30 seconds.
4. Stir in the flour and cook for about 1 minute. Gradually whisk in the milk and heavy cream, then simmer for 3–5 minutes until lightly thickened; season with black pepper and optional nutmeg.
5. Remove the sauce from the heat and stir in the Gruyere and about 1/4 cup of the Parmesan until smooth and melted.
6. Arrange half of the zucchini in the prepared dish. Spoon over half of the cheese sauce, then repeat with the remaining zucchini and sauce.
7. Mix the breadcrumbs with the remaining Parmesan and the olive oil or melted butter. Scatter this mixture evenly over the gratin.
8. Bake for approximately 35–45 minutes, until the zucchini is tender and the sauce is bubbling. Broil for 1–3 minutes at the end if you want a deeper golden crust, then rest for 10 minutes before serving.

Notes

Salt and dry the zucchini thoroughly to prevent excess liquid. Use a shallow dish and avoid stacking the slices too thickly so the gratin cooks and browns evenly.

Final Thoughts

The cheesiest zucchini gratin in the world earns its name honestly: every tender round is wrapped in creamy Gruyere sauce, supported by savory onion and garlic, and crowned with a Parmesan breadcrumb crust. The method is straightforward, but salting the zucchini, drying it well, and choosing a shallow dish make the difference between a watery casserole and a beautifully set gratin.

Give the finished dish its full 10-minute rest before serving, then bring it to the table while the crust is still crisp and the center is warm. It is an irresistible way to turn everyday summer squash into a memorable side dish for family dinners, holidays, and relaxed weekend meals.