Easy Zucchini Au Gratin Recipe

Easy Zucchini Au Gratin Recipe tastes rich, cheesy, and cozy with tender slices of zucchini under a golden, bubbly topping. It works perfectly for busy weeknights or holiday dinners and takes about 45 minutes from start to finish. I first made this on a sweltering August night in my tiny apartment kitchen and still loved it enough to keep it in my regular rotation.

Why You Should Try This Easy Zucchini Au Gratin Recipe

This zucchini au gratin recipe gives you all the comfort of potatoes au gratin with a lighter, veggie-forward twist. The zucchini turns silky in the oven, the cheese turns crisp on top, and the whole thing tastes like summer met a casserole dish.

You can use up a big garden haul or that bag of zucchini you impulse-bought at the store. The recipe uses simple ingredients, comes together quickly, and works as a side dish or a meatless main with a salad.

“Creamy, cheesy, and full of flavor, this Easy Zucchini Au Gratin Recipe turned my picky veggie-hater into a fan. ★★★★★”

Ingredients You’ll Need

Fresh ingredients

• 3 medium zucchini, thinly sliced into rounds (about 1/8 inch thick)
• 1 small yellow onion, very thinly sliced
• 2 cloves garlic, minced
• 2 tablespoons fresh parsley, chopped (optional but adds freshness)

Dairy and pantry ingredients

• 1 cup heavy cream
  • You can swap half-and-half for a lighter version, though the sauce turns slightly thinner.
• 1 cup shredded Gruyère cheese
  • Use Swiss cheese if you cannot find Gruyère.
• 1/2 cup shredded sharp cheddar cheese
  • Pre-shredded works, but freshly shredded melts smoother.
• 1/4 cup grated Parmesan cheese
  • Shelf-stable grated Parmesan works in a pinch, but real Parmigiano Reggiano gives better flavor.
• 2 tablespoons unsalted butter
• 1 tablespoon olive oil
• 2 tablespoons all-purpose flour
• 1/2 teaspoon dried thyme or Italian seasoning
• 1/4 teaspoon garlic powder
• 1/4 teaspoon onion powder
• 1/4 teaspoon smoked paprika or regular paprika
• Salt and black pepper to taste

Crunchy topping

• 1/2 cup panko breadcrumbs
  • Regular breadcrumbs work, but panko gives a crispier topping.
• 1 tablespoon melted butter
• 2 tablespoons grated Parmesan cheese

Equipment list

• 9×9 inch baking dish or similar size casserole dish
• Large skillet or sauté pan
• Cutting board and sharp knife or mandoline slicer
• Mixing bowls
• Whisk
• Aluminum foil
• Oven preheated to 400°F (200°C)

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 reduce extra moisture and keep the sauce thick.
• Use a mix of cheeses for the best flavor; Gruyère or Swiss for melt, cheddar for sharpness, Parmesan for salty nuttiness.
• Season each layer lightly with salt and pepper so the whole dish tastes well seasoned.
• Keep the cream warm before it goes into the oven so the casserole starts bubbling faster.
• Cover the dish with foil for the first part of baking, then uncover to brown the top.
• Broil for 1 to 2 minutes at the end if you want extra color on the cheese and breadcrumb topping.
• Let the zucchini au gratin rest 10 minutes before serving so the sauce thickens and slices hold together.

How to Make Easy Zucchini Au Gratin Recipe

Prep the zucchini and pan

1. Preheat your oven to 400°F (200°C).
2. Grease your baking dish with a little butter or olive oil.
3. Slice the zucchini into thin rounds and pat them dry with paper towels.
4. Slice the onion very thin so it softens quickly in the oven.

Cook the onion and garlic

1. Heat the olive oil and 1 tablespoon butter in a large skillet over medium heat.
2. Add the sliced onion and a pinch of salt, then cook until the onion turns soft and lightly golden, about 6 to 8 minutes.
3. Stir in the minced garlic and cook 30 seconds until fragrant, then remove the skillet from the heat.

Make the creamy cheese sauce

1. In the same skillet, add the remaining 1 tablespoon butter and let it melt over medium heat.
2. Whisk in the flour and cook 1 to 2 minutes until the mixture looks smooth and slightly foamy.
3. Slowly pour in the heavy cream while you whisk, so no lumps form.
4. Add thyme, garlic powder, onion powder, smoked paprika, salt, and pepper.
5. Simmer the sauce for 2 to 3 minutes until it thickens slightly.
6. Turn off the heat and stir in Gruyère and cheddar until they melt into a smooth sauce.

Layer the zucchini au gratin

1. Spread a spoonful of cheese sauce on the bottom of the baking dish.
2. Arrange a layer of zucchini slices over the sauce, slightly overlapping them.
3. Scatter some of the cooked onions over the zucchini.
4. Spoon more cheese sauce over the top, then repeat with another layer of zucchini, onion, and sauce.
5. Continue until you use all the zucchini and sauce, finishing with sauce on top.
6. Sprinkle grated Parmesan over the top layer.

Add the crunchy topping

1. In a small bowl, mix panko breadcrumbs, melted butter, and Parmesan.
2. Stir until the crumbs look evenly coated and slightly clumpy.
3. Sprinkle this mixture evenly over the top of the casserole.

Bake to golden perfection

1. Cover the baking dish loosely with foil, tenting it so it does not touch the topping.
2. Bake for 20 minutes, then remove the foil.
3. Continue baking 10 to 15 minutes until the zucchini turns tender and the top looks golden and bubbly.
4. If you want deeper browning, switch the oven to broil for 1 to 2 minutes and watch closely.
5. Remove the dish from the oven and let it rest 10 minutes before serving.
6. Sprinkle chopped fresh parsley over the top if you like a pop of color.

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. You can serve it alongside a crisp green salad with lemony dressing to balance the richness. It also tastes great with roasted carrots, steamed green beans, or a bowl of tomato soup. If you want a cozy vegetarian meal, add some crusty bread and a big salad and call it dinner.

Storage Options

• Store leftovers in an airtight container in the fridge for up to 3 days.
• Reheat individual portions in the microwave in 30 second bursts until hot, then finish under the broiler for 1 to 2 minutes to crisp the top.
• Reheat a larger portion in a 350°F oven, covered, for 15 to 20 minutes, then uncover for 5 minutes.
• Freeze tightly wrapped portions for up to 2 months, then thaw overnight in the fridge before reheating in the oven.

Easy Zucchini Au Gratin Recipe

Easy Zucchini Au Gratin tastes rich, cheesy, and cozy with tender slices of zucchini under a golden, bubbly topping, perfect as a comforting side dish or a meatless main with a salad.

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Prep Time 15 minutes mins

Cook Time 30 minutes mins

Total Time 45 minutes mins

Servings: 6

Course: Dinner

Ingredients

  

• 3 medium zucchini, thinly sliced into 1/8-inch rounds
• 1 small yellow onion, very thinly sliced
• 2 cloves garlic, minced
• 2 tablespoons fresh parsley, chopped

• 1 cup heavy cream
• 1 cup shredded Gruyère cheese
• 1/2 cup shredded sharp cheddar cheese
• 1/4 cup grated Parmesan cheese
• 2 tablespoons unsalted butter
• 1 tablespoon olive oil
• 2 tablespoons all-purpose flour
• 1/2 teaspoon dried thyme or Italian seasoning
• 1/4 teaspoon garlic powder
• 1/4 teaspoon onion powder
• 1/4 teaspoon smoked paprika or regular paprika
• Salt and black pepper, to taste

• 1/2 cup panko breadcrumbs
• 1 tablespoon melted butter
• 2 tablespoons grated Parmesan cheese

Instructions

 

1. Preheat your oven to 400°F (200°C).
2. Grease a 9x9-inch baking dish or similar casserole dish with a little butter or olive oil.
3. Slice the zucchini into thin 1/8-inch rounds and pat them dry with paper towels to remove excess moisture.
4. Slice the onion very thin so it softens quickly in the oven.

1. Heat the olive oil and 1 tablespoon of the butter in a large skillet over medium heat.
2. Add the sliced onion and a pinch of salt, then cook until the onion is soft and lightly golden, about 6 to 8 minutes.
3. Stir in the minced garlic and cook for about 30 seconds until fragrant, then remove the skillet from the heat and transfer the onions and garlic to a bowl.

1. In the same skillet, add the remaining 1 tablespoon butter and melt over medium heat.
2. Whisk in the flour and cook for 1 to 2 minutes until the mixture looks smooth and slightly foamy.
3. Slowly pour in the heavy cream while whisking constantly so no lumps form.
4. Stir in the dried thyme or Italian seasoning, garlic powder, onion powder, smoked paprika, salt, and black pepper.
5. Simmer the sauce for 2 to 3 minutes, whisking often, until it thickens slightly.
6. Turn off the heat and stir in the Gruyère and cheddar until they melt into a smooth, creamy sauce.

1. Spread a spoonful of the cheese sauce over the bottom of the prepared baking dish.
2. Arrange a layer of zucchini slices over the sauce, slightly overlapping the rounds.
3. Scatter some of the cooked onions and garlic over the zucchini.
4. Spoon more cheese sauce over the top, then repeat with another layer of zucchini, onions, and sauce.
5. Continue layering until you use all the zucchini and sauce, finishing with a layer of sauce on top.
6. Sprinkle the 1/4 cup grated Parmesan evenly over the top layer of sauce.

1. In a small bowl, combine the panko breadcrumbs, melted butter, and 2 tablespoons grated Parmesan.
2. Stir until the crumbs look evenly coated and slightly clumpy.
3. Sprinkle the breadcrumb mixture evenly over the top of the casserole.

1. Cover the baking dish loosely with aluminum foil, tenting it so it does not touch the topping.
2. Bake for 20 minutes, then remove the foil.
3. Continue baking for 10 to 15 minutes more, until the zucchini is tender and the top is golden and bubbly.
4. If you want deeper browning, switch the oven to broil for 1 to 2 minutes, watching closely so it does not burn.
5. Remove the dish from the oven and let it rest for 10 minutes so the sauce thickens and the slices hold together.
6. Sprinkle with chopped fresh parsley before serving, if using.

Notes

Nutrition Information
Approximate per serving (1/6 of recipe): 260–300 calories; fat 22 g; saturated fat 13 g; carbohydrates 9 g; fiber 2 g; sugars 4 g; protein 9 g; sodium 330 mg. Values will vary based on specific ingredients, brands, and portion sizes.