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This cheesy zucchini gratin is layered with a quick, creamy garlic sauce, mozzarella, and Parmesan, then baked until golden and bubbly. The secret is cooking the moisture out of the zucchini first, so this zucchini au gratin turns out creamy and never watery. It’s an easy zucchini side dish that goes with just about any dinner.
This cheesy zucchini gratin is the side dish that gets my kids to happily eat their vegetables. Tender zucchini is layered with a quick, creamy garlic sauce, mozzarella, and Parmesan, then baked until the top is golden and bubbly. The best part? It’s never watery, because we cook the moisture out of the zucchini on the stovetop before it ever goes in the oven.
Zucchini is one of our favorite vegetables to eat on the side of chicken or steak. This zucchini gratin would even be a perfect side dish on Thanksgiving or if you have an abundance of zucchini growing in your garden.
If you love gratins, check out my Cauliflower Gratin and Cheesy Potatoes au Gratin. If you love mac and cheese, check out my Best Macaroni and Cheese Recipe.
Why You’ll Love This Zucchini Gratin
- Never watery. Cooking the zucchini first gets rid of the extra moisture, so the sauce stays creamy.
- One skillet for the filling. The zucchini and the sauce are made in the same pan.
- Simple ingredients. Zucchini, onion, garlic, butter, flour, milk, and cheese.
- Fancy enough for guests. It looks and tastes like a restaurant side but is easy enough for a weeknight.
Zucchini Gratin Ingredients
- Zucchini: Choose small to medium zucchini. They have fewer seeds and less water than large ones. No need to peel.
- Butter: For sautéing the onion and building the sauce.
- Onion and garlic: Add a sweet, savory base of flavor. If you don’t want to use fresh garlic, I like to use the frozen garlic cubes from stores like Trader Joe’s.
- Salt and pepper: Season the zucchini as it cooks. I like layering flavors and making sure the zucchini has enough talt.
- Flour: Thickens the milk into a creamy sauce that coats the zucchini.
- Whole milk: Makes the sauce rich and creamy. You can use half-and-half for an even richer gratin.
- Mozzarella: Use low-moisture mozzarella (not fresh) for that gooey, golden top. For more flavor, swap half for Gruyère.
- Parmesan: Adds a salty, nutty flavor and helps the top get crispy.
- Optional seasonings: A pinch of nutmeg (classic in gratins) or a little thyme or Italian seasoning.
How to Keep Zucchini Gratin From Getting Watery
Zucchini is about 95% water, which is why so many zucchini gratins and casseroles end up soupy. Here’s how to prevent it:
- Cook the zucchini first. Sauté the zucchini slices until the liquid they release has mostly cooked off. This is the most important step.
- Drain it well. Move the cooked zucchini to a paper towel-lined plate so any extra liquid doesn’t end up in the dish.
- Make the sauce separately. A thick cream sauce made on its own won’t get thinned out by zucchini juices.
- Slice evenly. Cut the zucchini into ¼-inch rounds so they cook at the same rate. Slices that are too thin turn mushy.
- Use low-moisture mozzarella. Fresh mozzarella releases water as it bakes.
- Bake uncovered. Covering traps steam and makes the gratin wet.
- Let it rest. Resting 5 to 10 minutes after baking lets the sauce set up.
How to Make Zucchini Gratin
- Prep. Preheat the oven to 375°F and grease a small (about 1-quart) baking dish.
- Cook the vegetables. Melt 1 tablespoon butter in a large skillet over medium heat. Add the onion and cook 3 to 4 minutes until soft, then add the garlic and cook 30 seconds.
- Cook the zucchini. Add the zucchini, salt, and pepper. Cook 5 to 8 minutes, stirring occasionally, until the zucchini is just tender and most of the liquid has cooked off. Transfer to a paper towel-lined plate to drain.
- Make the cream sauce. Wipe out the skillet. Melt the remaining 2 tablespoons butter, whisk in the flour, and cook 1 minute. Slowly whisk in the milk and cook 2 to 3 minutes, whisking, until thick and creamy. Remove from the heat and stir in ¼ cup Parmesan and the nutmeg or herbs, if using.
- Layer. Spread half the zucchini in the dish and spoon half the sauce over it. Sprinkle with ⅓ cup mozzarella and 2 tablespoons Parmesan. Repeat with the remaining zucchini, sauce, and cheese.
- Bake. Bake uncovered for 20 to 25 minutes until bubbly. Broil 1 to 2 minutes for a deeper golden top, watching closely.
- Rest. Let it rest 5 to 10 minutes before serving.
Tips for the Best Cheesy Zucchini Gratin
- Shred your own cheese. Pre-shredded cheese has anti-caking agents that keep it from melting as smoothly.
- Use a shallow dish. More surface area means more golden, cheesy top.
- Season well. Zucchini is mild, so taste the sauce before layering and add more salt if needed.
- Add a crunchy topping. Toss ¼ cup panko with 1 tablespoon melted butter and sprinkle on top before baking.
- Double it. Double the recipe and bake it in a 9×13-inch dish for a crowd. Add 5 to 10 minutes to the bake time.
Zucchini Gratin FAQ’s:
How do you keep zucchini gratin from getting watery? Cook the zucchini on the stovetop until the liquid it releases has mostly evaporated, drain any extra, use low-moisture mozzarella, and bake uncovered.
Do you peel zucchini for gratin? No. The skin is tender, adds color, and helps the slices hold their shape.
What’s the difference between gratin and au gratin? Nothing. “Au gratin” means “with a gratin,” or with a browned, cheesy top, so zucchini gratin and zucchini au gratin are the same dish.
What cheese is best for zucchini gratin? Low-moisture mozzarella melts beautifully, and Parmesan adds flavor and a crispy top. Gruyère is a great swap for half the mozzarella.
Can I make zucchini gratin ahead of time? Yes. Assemble it up to 1 day ahead and refrigerate, then bake when you’re ready.
Can I freeze zucchini gratin? It’s not recommended, since the zucchini becomes watery and soft after thawing.
Can I use yellow squash? Yes. Yellow squash works the same way, or use a mix of both.
What to Serve With Zucchini Gratin
- The Best Chicken Marinade: Grilled or baked chicken with our most popular marinade is the perfect easy pairing for a creamy, cheesy gratin.
- Baked Caprese Chicken: Juicy chicken with tomatoes, mozzarella, and balsamic.
- Marry Me Chicken: Creamy sun-dried tomato chicken for a cozy dinner.
- Tri-tip Steak: How to make the best tri-tip steak marinade.
- Honey Chicken: Sweet and savory chicken that balances the rich gratin.
- Smoked Turkey Breast: This is a boneless, skinless turkey breast cooked on a smoker.
More Zucchini Recipes:
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Cheesy Zucchini Gratin
Ingredients
- 3 Tablespoons Butter divided
- 1 small Onion diced
- 1 clove Garlic minced
- 1 lb. Zucchini about 2 medium, sliced into ¼-inch rounds
- 1/2 to 1 teaspoon Salt
- 1/2 teaspoon Pepper
- 2 Tablespoons All-Purpose Flour
- 3/4 cup Whole Milk
- Pinch Nutmeg optional
- 1 to 1 1/2 cups Mozzarella Cheese or half Gruyère, divided
- 1/2 cup grated Parmesan divided
Instructions
- Preheat the oven to 375°F. Grease a 1-quart baking dish.
- Melt 1 tablespoon butter in a large skillet over medium heat. Cook the onion 3 to 4 minutes, then add the garlic and cook 30 seconds.
- Add the zucchini, salt, and pepper. Cook 5 to 8 minutes until just tender and most of the liquid has cooked off. Transfer to a paper towel-lined plate to drain.
- Wipe out the skillet. Melt the remaining 2 tablespoons butter, whisk in the flour, and cook 1 minute. Slowly whisk in the milk and cook 2 to 3 minutes until thickened. Remove from the heat and stir in ¼ cup Parmesan and the nutmeg or herbs, if using.
- Layer half the zucchini in the dish, spoon over half the sauce, and sprinkle with ⅓ cup mozzarella and 2 tablespoons Parmesan. Repeat with the remaining zucchini, sauce, and cheese.
- Bake uncovered 20 to 25 minutes until bubbly. Broil 1 to 2 minutes until golden. Rest 5 to 10 minutes before serving.
Notes
- Use small to medium zucchini for less water and fewer seeds.
- Shred your own cheese for the smoothest melt.
- For a 9×13-inch dish, double the recipe and add 5 to 10 minutes to the bake time.
- Make ahead: assemble up to 1 day ahead, refrigerate, and add 5 to 10 minutes to the bake time.
Nutrition
Nutrition information is automatically calculated, so should only be used as an approximation.
