Zucchini Gratin with Yellow Squash

Imagine the irresistible aroma of bubbling cheese mingling with tender slices of summer squash, all topped with a golden, crispy crust that crackles under your fork. This Zucchini Gratin with Yellow Squash transforms humble garden vegetables into a sophisticated side dish that’s both comforting and elegant. The natural sweetness of zucchini and yellow squash creates a perfect canvas for savory herbs and rich dairy, resulting in a dish that’s sure to impress even vegetable skeptics. You’ll learn how to create layers of flavor that make this gratin memorable, versatile, and absolutely delicious.

Why You’ll Love This Recipe

This Zucchini Gratin with Yellow Squash is the perfect balance of healthy vegetables and indulgent comfort food. The contrast between the tender, melt-in-your-mouth squash and the crispy, golden breadcrumb topping creates an irresistible textural experience that keeps you coming back for more.

What makes this gratin special is how it elevates simple summer produce into something truly spectacular. The zucchini and yellow squash maintain their delicate flavors while absorbing the rich, creamy sauce that surrounds them. Fragrant herbs and just the right amount of cheese provide depth without overwhelming the vegetables themselves.

Beyond the incredible taste, this dish is remarkably versatile. It works beautifully as a side dish for holiday meals but is simple enough for weeknight dinners. It can be prepped ahead, making entertaining stress-free, and it pairs wonderfully with everything from grilled meats to roasted fish. Whether you’re looking to use up a garden surplus or simply want to incorporate more vegetables into your meals, this squash gratin delivers both nutrition and indulgence in every bite.

Ingredients

For this delicious Zucchini Gratin with Yellow Squash, you’ll need:

• 2 medium zucchini (about 1 lb/450g), sliced into ¼-inch rounds
• 2 medium yellow squash (about 1 lb/450g), sliced into ¼-inch rounds
• 1 medium onion (about 8 oz/225g), thinly sliced
• 2 cloves garlic, minced
• 2 tablespoons (30ml) olive oil
• 1 cup (240ml) heavy cream
• 2 large eggs, beaten
• 1 cup (100g) grated Gruyère cheese (Swiss cheese works as a substitute)
• ½ cup (50g) freshly grated Parmesan cheese, divided
• 1 tablespoon fresh thyme leaves (or 1 teaspoon dried)
• 1 teaspoon fresh rosemary, finely chopped (or ½ teaspoon dried)
• ½ cup (60g) panko breadcrumbs
• 2 tablespoons (30g) unsalted butter, melted
• Salt and freshly ground black pepper to taste

Choose firm, unblemished zucchini and yellow squash for the best texture in your gratin. The combination of Gruyère and Parmesan provides the perfect balance of creaminess and nutty flavor that complements the summer squash beautifully.

Pro Tips

Avoid Soggy Gratin: The key to a perfect Zucchini Gratin with Yellow Squash is managing moisture. Salt your sliced squash and let it sit for 15-20 minutes before cooking. Then pat the pieces dry with paper towels to draw out excess water. This crucial step prevents your gratin from becoming watery and ensures that crispy, golden top we’re all after.

Perfect Your Layers: When assembling your gratin, slightly overlap the squash slices rather than piling them haphazardly. This technique creates even cooking and allows the cream mixture to distribute perfectly throughout the dish. The result is a consistently tender texture with no undercooked spots.

Temperature Matters: Start baking your squash gratin covered at a moderate temperature (350°F/175°C) to gently cook the vegetables and allow flavors to meld. Then uncover and increase to 425°F (220°C) for the final 10-15 minutes. This two-step process ensures your vegetables are thoroughly cooked while still achieving that irresistible golden-brown crust on top. Letting the gratin rest for 10 minutes before serving allows the custard to set properly, making it easier to serve beautiful portions.

Instructions

Step 1

Preheat your oven to 350°F (175°C) and grease a 9×13-inch baking dish. Slice your zucchini and yellow squash into ¼-inch rounds, then place them in a colander. Sprinkle with 1 teaspoon salt and toss gently. Let stand for 15-20 minutes to release excess moisture. While waiting, thinly slice your onion and mince the garlic.

Step 2

Pat the squash dry with paper towels to remove surface moisture. In a large skillet over medium heat, warm the olive oil, then add the sliced onions. Cook for 5-6 minutes until they become translucent and start to caramelize slightly. Add the minced garlic and cook for another 30 seconds until fragrant. Remove from heat and let cool slightly.

Step 3

In a medium bowl, whisk together the heavy cream and beaten eggs. Stir in the grated Gruyère, half of the Parmesan cheese, thyme, rosemary, ½ teaspoon salt, and ¼ teaspoon black pepper. The mixture should be rich and fragrant, perfectly seasoned to complement your Zucchini Gratin with Yellow Squash.

Step 4

Layer half of the squash slices in the prepared baking dish, slightly overlapping them. Spread the sautéed onion and garlic mixture evenly over the squash. Arrange the remaining squash slices on top, creating an attractive pattern. Slowly pour the cream and cheese mixture over everything, allowing it to seep between the layers.

Step 5

In a small bowl, mix the panko breadcrumbs with the remaining Parmesan cheese and melted butter. This will create the perfect crispy topping. Sprinkle this mixture evenly over the top of your gratin. Cover the dish with aluminum foil, being careful not to let it touch the topping.

Step 6

Bake covered for 30 minutes, then remove the foil and increase the oven temperature to 425°F (220°C). Bake for an additional 15 minutes until the top is golden brown and crispy, and the gratin is bubbling around the edges. Allow your Zucchini Gratin with Yellow Squash to rest for 10 minutes before serving to set properly and cool slightly.

Variations

Mediterranean Zucchini Gratin: Transform your Zucchini Gratin with Yellow Squash with Mediterranean flavors by adding ½ cup of pitted, chopped Kalamata olives and ¼ cup of sun-dried tomatoes to the vegetable mixture. Replace the Gruyère with crumbled feta cheese and add 1 tablespoon of dried oregano to the herb blend. Finish with a sprinkle of toasted pine nuts over the breadcrumb topping for added texture and nutty flavor.

Dairy-Free Summer Squash Gratin: Create a delicious dairy-free version by substituting the heavy cream with 1 cup of full-fat coconut milk whisked with 1 tablespoon of nutritional yeast for a cheesy flavor. Replace the butter with olive oil and use a mixture of seasoned gluten-free breadcrumbs and nutritional yeast in place of the cheese topping. The result is a lighter yellow squash and zucchini bake that maintains all the comfort of the original.

Spicy Southwest Gratin: Add a kick to your squash gratin by incorporating 1 diced jalapeño, ½ cup corn kernels, and ½ teaspoon of ground cumin to the vegetable mixture. Replace the Gruyère with pepper jack cheese and top with crushed tortilla chips mixed with the Parmesan for extra crunch and flavor. Serve with a dollop of sour cream and chopped cilantro for a Southwestern-inspired side dish.

Storage/Serving

This Zucchini Gratin with Yellow Squash can be refrigerated in an airtight container for up to 3 days. For best results when reheating, cover with foil and warm in a 325°F (165°C) oven for 15-20 minutes until heated through, removing the foil for the last 5 minutes to re-crisp the top. Avoid microwaving if possible, as it can make the topping soggy.

Serve this elegant gratin alongside roasted chicken or grilled lamb chops for a complete meal that highlights the summer squash. For a vegetarian feast, pair it with a simple green salad dressed with lemon vinaigrette and some crusty artisan bread to soak up the creamy sauce.

This dish also makes a wonderful addition to brunch when served with poached eggs on top. The runny yolks create a luxurious sauce that complements the creamy squash beautifully. For entertaining, prepare the gratin up to the baking stage a day ahead, refrigerate, and simply bake when guests arrive for a stress-free, impressive side dish.

FAQs

Can I make this Zucchini Gratin ahead of time?
Yes! You can assemble the entire gratin up to 24 hours in advance, cover and refrigerate. When ready to bake, let it sit at room temperature for 30 minutes, then follow the baking instructions, adding an extra 5-10 minutes to the covered baking time.

My gratin turned out watery. What went wrong?
The most common cause is skipping the salting step. Always salt your sliced squash and let it sit to release moisture, then pat dry thoroughly. Additionally, make sure to let your gratin rest for at least 10 minutes after baking to set properly.

Can I freeze this squash gratin?
While possible, freezing isn’t ideal as the squash can become mushy and release more water when thawed. If you must freeze, do so after baking and cooling completely. Thaw overnight in the refrigerator and reheat covered at 325°F until heated through.

What can I substitute for Gruyère cheese?
Swiss cheese is the closest substitute. Other good options include Emmental, Jarlsberg, or even a combination of mozzarella and Parmesan for a different but delicious flavor profile.

Is there a way to make this lower in calories?
Yes, you can substitute half-and-half for the heavy cream and reduce the cheese by half. The texture won’t be quite as rich, but you’ll still have a delicious gratin with fewer calories.

Conclusion

This Zucchini Gratin with Yellow Squash is comfort food at its finest — a perfect balance of garden-fresh vegetables and indulgent creaminess that elevates humble summer squash into something truly special. It’s the kind of dish that brings everyone to the table with its golden, crispy top and tender, flavorful interior. Whether you’re serving it for a holiday gathering or a simple family dinner, this versatile gratin proves that vegetables can be the star of any meal when prepared with care and quality ingredients. Make this recipe your own with the suggested variations, and you’ll have a reliable, crowd-pleasing dish in your repertoire for years to come.

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