Easy Zucchini Au Gratin Recipe tastes rich, cheesy, and cozy, with tender zucchini tucked under a golden, bubbly top. It works perfectly for busy weeknights or holiday dinners and takes about 45 minutes from start to finish. I tested this on my picky neighbor’s kids, and they asked for seconds before they noticed the zucchini.
Why You Should Try This Easy Zucchini Au Gratin Recipe
This Easy Zucchini Au Gratin Recipe gives you creamy comfort food without feeling heavy. The zucchini turns soft and silky, the cheese turns melty and browned, and the whole thing tastes like scalloped potatoes that went on a summer vacation.
You can use up extra garden zucchini, toss everything into one baking dish, and let the oven handle the hard work. The recipe fits low-stress entertaining, meal prep, or a “clean out the crisper” night.
“This Easy Zucchini Au Gratin Recipe tastes like a fancy steakhouse side, but I made it on a Tuesday in yoga pants. ★★★★★”
Ingredients You’ll Need
Fresh produce
- 3 medium zucchini, thinly sliced into rounds (about 1/8 inch thick)
- 1 small yellow onion, very thinly sliced
- 2 cloves garlic, minced (use jarred minced garlic as a shortcut if you like)
- 1 tablespoon fresh thyme leaves, chopped
- Use 1 teaspoon dried thyme if you do not have fresh herbs.
Dairy
- 1 cup heavy cream
- Use half-and-half for a lighter version, but the sauce turns slightly less thick.
- 1/2 cup whole milk
- 1 1/2 cups shredded Gruyère cheese
- Use Swiss cheese or a Swiss and mozzarella blend if Gruyère costs too much or you cannot find it.
- 1/2 cup freshly grated Parmesan cheese
- Pre-grated Parmesan from a good brand works, but avoid the shelf-stable shaker style for this.
Pantry items
- 2 tablespoons unsalted butter
- 1 tablespoon olive oil
- 2 tablespoons all-purpose flour
- 1/2 teaspoon kosher salt, plus more to taste
- 1/2 teaspoon black pepper
- 1/4 teaspoon smoked paprika or regular paprika
- 1/4 teaspoon garlic powder (optional, for extra flavor)
- 1/4 teaspoon onion powder (optional)
- 1/3 cup panko breadcrumbs
- Use regular breadcrumbs if that is what you have; panko gives more crunch.
- Cooking spray or a little extra butter or oil for greasing the baking dish
Equipment
- 9×13 inch baking dish or similar size casserole dish
- Large skillet or sauté pan
- Medium saucepan
- Cutting board and sharp knife or mandoline slicer
- Whisk
- Measuring cups and spoons
- Aluminum foil
Tips & Tricks
- Slice the zucchini evenly so it cooks at the same rate and stays tender, not mushy.
- Pat the zucchini slices dry with paper towels to remove extra moisture and keep the sauce thick.
- Use a mix of Gruyère and Parmesan for the best flavor; the Gruyère melts smoothly and the Parmesan adds a salty kick.
- Grate cheese from a block instead of using pre-shredded bags, since bagged cheese often includes starch that makes the sauce grainy.
- Layer the zucchini slightly overlapping, like shingles, so the cream and cheese coat every slice.
- Taste the cream sauce before you pour it over the zucchini and adjust salt and pepper right then.
- Cover the dish with foil for the first part of baking so the zucchini softens, then remove it so the top browns.
- If the top browns too fast, tent the dish loosely with foil again near the end.
- Let the zucchini au gratin rest 10 minutes before serving so the sauce thickens and slices hold together.
- Use a mandoline carefully if you want super thin, even slices; always use the guard and keep fingers away from the blade.
How to Make Easy Zucchini Au Gratin Recipe
Step 1: Prep the zucchini and aromatics
Wash the zucchini and trim the ends. Slice the zucchini into thin rounds, about 1/8 inch thick, and pat them dry with paper towels. Thinly slice the onion and mince the garlic.
Grease your baking dish with cooking spray, butter, or a little olive oil. Preheat your oven to 400°F so it heats while you prep the sauce.
Step 2: Sauté veggies and aromatics
Heat the olive oil and 1 tablespoon of butter in a large skillet over medium heat. Add the sliced onion and cook until soft and lightly golden, about 6 to 8 minutes, and stir often. Add the minced garlic and thyme, then cook 1 minute until the garlic smells fragrant.
Take the skillet off the heat. Set the onion mixture aside while you make the creamy cheese sauce.
Step 3: Make the creamy cheese sauce
Melt the remaining 1 tablespoon of butter in a medium saucepan over medium heat. Whisk in the flour and cook 1 to 2 minutes, until the mixture looks smooth and slightly foamy, and keep whisking so it does not burn. Pour in the heavy cream and milk slowly while you whisk, and keep whisking until the mixture looks smooth.
Add salt, black pepper, smoked paprika, garlic powder, and onion powder. Simmer the sauce 3 to 4 minutes, and whisk often, until it thickens enough to coat the back of a spoon. Turn off the heat, then stir in 1 cup of Gruyère and 1/4 cup of Parmesan until they melt and the sauce turns silky.
Taste the sauce and adjust salt and pepper. The sauce should taste slightly more seasoned than you want the final dish, since the zucchini adds mild flavor.
Step 4: Layer the zucchini and onions
Spread half of the sautéed onions in an even layer on the bottom of the greased baking dish. Arrange half of the zucchini slices on top in slightly overlapping rows. Scatter the remaining onions over the zucchini, then top with the rest of the zucchini slices.
Pour the warm cheese sauce evenly over the zucchini and onions. Gently shake the dish or tap it on the counter so the sauce settles into all the gaps.
Step 5: Add cheesy breadcrumb topping
In a small bowl, mix the remaining 1/2 cup Gruyère, 1/4 cup Parmesan, and panko breadcrumbs. Add a pinch of salt and pepper if you like. Sprinkle this mixture evenly over the top of the sauced zucchini.
Lightly spray the top with cooking spray or drizzle a tiny bit of olive oil to help the topping crisp. Cover the dish loosely with foil, and avoid pressing it down onto the cheese.
Step 6: Bake until bubbly and golden
Bake the zucchini au gratin at 400°F for 20 minutes with the foil on. Remove the foil and bake another 10 to 15 minutes, until the top turns golden and the sauce bubbles around the edges. If you want extra color, place the dish under the broiler for 1 to 2 minutes, and watch closely so it does not burn.
Set the dish on a cooling rack and let it rest 10 minutes. This short rest helps the sauce thicken and makes serving much easier.
Step 7: Serve and enjoy
Use a large spoon or spatula to scoop generous portions. The zucchini should feel tender but not fall apart, and the top should taste crunchy and cheesy. Garnish with extra thyme or chopped parsley if you want a fresh pop of color.
Serve the Easy Zucchini Au Gratin Recipe hot while the cheese still stretches. Expect people to ask where you hid the potatoes.
What to Serve with Easy Zucchini Au Gratin Recipe
This Easy Zucchini Au Gratin Recipe pairs nicely with simple grilled chicken, roasted turkey breast, or baked salmon-style fillets. You can also serve it with a crisp green salad, roasted carrots, or steamed green beans for a full plate. If you want a vegetarian meal, add a pot of lentils, chickpeas, or a hearty bean salad on the side.
Kids often enjoy this with buttered noodles or garlic bread, since the cheesy sauce feels familiar. A cold glass of sparkling water with lemon or iced herbal tea balances the richness.
Storage Options
- Store leftovers in an airtight container in the fridge for up to 3 to 4 days.
- Reheat single portions in the microwave in 30 second bursts until hot, then crisp the top under the broiler for 1 to 2 minutes if you want.
- Reheat a larger portion in a 350°F oven, covered with foil, for 15 to 20 minutes, then uncover for 5 minutes to crisp.
- Freeze tightly wrapped portions for up to 2 months, thaw overnight in the fridge, and reheat in the oven so the texture stays pleasant.
Easy Zucchini Au Gratin Recipe
Ingredients
Instructions
- Preheat the oven to 400°F (200°C). Grease a 9x13-inch baking dish with cooking spray, butter, or olive oil.
- Wash the zucchini, trim the ends, and slice into thin 1/8-inch rounds. Pat the slices dry with paper towels to remove excess moisture.
- Thinly slice the yellow onion and mince the garlic.
- Heat the olive oil and 1 tablespoon of the butter in a large skillet over medium heat.
- Add the sliced onion and cook, stirring often, until soft and lightly golden, about 6 to 8 minutes.
- Stir in the minced garlic and thyme and cook for 1 minute, just until fragrant. Remove the skillet from the heat and set the onion mixture aside.
- In a medium saucepan, melt the remaining 1 tablespoon butter over medium heat. Whisk in the flour and cook for 1 to 2 minutes, whisking constantly, until smooth and slightly foamy.
- Slowly pour in the heavy cream and whole milk while whisking until the mixture is smooth.
- Season with kosher salt, black pepper, smoked paprika, garlic powder, and onion powder. Simmer for 3 to 4 minutes, whisking often, until the sauce thickens enough to coat the back of a spoon.
- Turn off the heat and stir in 1 cup of the Gruyère and 1/4 cup of the Parmesan until melted and silky. Taste and adjust the seasoning; the sauce should be slightly more seasoned than you want the finished dish to be.
- Spread half of the sautéed onions evenly over the bottom of the prepared baking dish.
- Arrange half of the zucchini slices over the onions in slightly overlapping rows, like shingles.
- Scatter the remaining onions over the zucchini, then arrange the remaining zucchini slices on top in the same slightly overlapping pattern.
- Pour the warm cheese sauce evenly over the layered zucchini and onions. Gently shake or tap the dish so the sauce settles into all the gaps.
- In a small bowl, combine the remaining 1/2 cup Gruyère, remaining 1/4 cup Parmesan, and the panko breadcrumbs. Season with a small pinch of salt and pepper if desired.
- Sprinkle the cheese and breadcrumb mixture evenly over the top of the sauced zucchini.
- Lightly spray the topping with cooking spray or drizzle with a little olive oil to help it crisp. Cover the dish loosely with foil without pressing it down onto the cheese.
- Bake the zucchini au gratin at 400°F (200°C) for 20 minutes with the foil on.
- Remove the foil and bake for another 10 to 15 minutes, until the top is golden and the sauce is bubbling around the edges.
- For extra color, place the dish under the broiler for 1 to 2 minutes, watching closely so it does not burn.
- Transfer the baking dish to a cooling rack and let the gratin rest for about 10 minutes so the sauce thickens and the portions hold together when served.
- Use a large spoon or spatula to scoop generous portions of the zucchini au gratin. The zucchini should be tender but not falling apart, and the top should be crunchy and cheesy.
- Garnish with extra thyme or chopped parsley if desired, and serve hot.
Notes
Approximate per serving (1/6 of recipe): 280–320 calories; fat 24 g; saturated fat 14 g; carbohydrates 10 g; fiber 1 g; sugars 4 g; protein 9 g; sodium 420 mg. Values will vary based on exact ingredients, brands, and portion size.
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