This Zucchini and Yellow Squash Au Gratin is a comforting, creamy baked dish that turns simple summer vegetables into an elegant side or light main course. Tender squash slices are layered with a rich cream sauce, savory cheese, and baked until golden and bubbling, making it perfect for both everyday meals and special gatherings.

Why You’ll Love This Recipe

This recipe is easy to prepare yet feels indulgent and satisfying. It highlights fresh zucchini and yellow squash in a way that even picky eaters enjoy. The creamy cheese sauce pairs beautifully with the mild vegetables, while the optional breadcrumb topping adds a delightful crunch. It’s vegetarian-friendly, versatile, and works well as a side dish or a main paired with a fresh salad.

Ingredients

(Tip: You’ll find the full list of ingredients and measurements in the recipe card below.)

2 medium zucchinis, thinly sliced into rounds
2 medium yellow squashes, thinly sliced into rounds
1 tablespoon olive oil
1/2 cup diced onion
2 cloves garlic, minced
1 cup heavy cream
1/2 cup grated Parmesan cheese
1 cup shredded Gruyère or Swiss cheese, divided
1/2 teaspoon dried thyme
1/2 teaspoon salt, or to taste
1/4 teaspoon black pepper, or to taste
1/4 cup bread crumbs (optional, for topping)
1 tablespoon olive oil (for mixing with bread crumbs, optional)
2 tablespoons fresh parsley, finely chopped (for garnish)

Directions

Preheat your oven to 375°F (190°C). Lightly grease a 9×9-inch baking dish or a similar-sized oven-safe dish.

Heat 1 tablespoon of olive oil in a skillet over medium heat. Add the diced onion and cook for 3 to 4 minutes, stirring occasionally, until softened and translucent. Add the minced garlic and cook for about 30 seconds until fragrant. Remove from heat.

In a mixing bowl, combine the heavy cream, grated Parmesan cheese, 1/2 cup of the shredded Gruyère or Swiss cheese, dried thyme, cooked onion and garlic, salt, and black pepper. Stir until well combined.

Arrange half of the zucchini and yellow squash slices evenly in the bottom of the prepared baking dish. Pour half of the cream and cheese mixture over the vegetables, spreading it evenly. Layer the remaining squash slices on top and pour the rest of the sauce over them. Sprinkle the remaining 1/2 cup of shredded cheese evenly on top.

If using the breadcrumb topping, mix the bread crumbs with 1 tablespoon of olive oil and sprinkle evenly over the cheese layer.

Bake uncovered for 30 to 35 minutes, or until the top is golden and bubbly and the squash is tender when pierced with a fork.

Remove from the oven and let the dish rest for 5 to 10 minutes before serving. Garnish with chopped fresh parsley and serve warm.

Servings and timing

This recipe serves 4 to 6 people as a side dish or light main course.
Total time is approximately 45 to 50 minutes, including about 15 minutes of preparation and 30 to 35 minutes of baking time.

Variations

For a lighter version, replace the heavy cream with half-and-half or whole milk thickened with 1 teaspoon of cornstarch.
Add a pinch of ground nutmeg to the cream sauce for extra warmth and depth of flavor.
Stir in a small pinch of crushed red pepper flakes for a subtle spicy kick.
You can also mix in thinly sliced mushrooms or spinach layers for added vegetables.

Storage/Reheating

Store leftovers in an airtight container in the refrigerator for up to 3 days. To reheat, warm individual portions in the oven at 350°F (175°C) until heated through, or microwave gently in short intervals to avoid overcooking. The sauce may thicken slightly after chilling, but it will loosen as it reheats.

FAQs

Can I make this dish ahead of time?

Yes, you can assemble the gratin up to one day in advance, cover it tightly, and refrigerate. Bake just before serving.

Can I use only zucchini or only yellow squash?

Yes, you can use just one type of squash if that’s what you have. The texture and flavor will still be delicious.

What cheese can I use instead of Gruyère or Swiss?

Mozzarella, provolone, or a mild white cheddar can work well, though the flavor will be slightly different.

Is this dish gluten-free?

It can be gluten-free if you omit the bread crumbs or use gluten-free bread crumbs.

Can I freeze zucchini and yellow squash au gratin?

Freezing is not recommended, as the cream sauce may separate and the squash can become watery when thawed.

How do I prevent the dish from becoming watery?

Slice the squash evenly and avoid overbaking. Letting the gratin rest before serving also helps the sauce thicken.

Can I add protein to this recipe?

Yes, you can add cooked legumes or serve the gratin alongside a protein-based main dish.

What size baking dish works best?

A 9×9-inch baking dish or any similar-sized shallow dish works well for even cooking.

Can I use dried parsley instead of fresh?

Fresh parsley is best for garnish, but dried parsley can be used in smaller amounts if needed.

Is this suitable for a holiday table?

Absolutely. Its creamy texture and golden top make it a great addition to festive meals.

Conclusion

Zucchini and Yellow Squash Au Gratin is a simple yet elegant recipe that celebrates fresh vegetables with rich, comforting flavors. Whether served as a side dish or a light vegetarian main, it’s a reliable crowd-pleaser that’s easy to customize and perfect for any occasion.

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