Name: Zucchini and Yellow Squash Au Gratin
Prep time: 20 min
Cook time: 30 min
Total time: 60 min
Ingredients: 2 medium zucchinis (thinly sliced); 2 medium yellow squash (thinly sliced); 1 small yellow onion (thinly sliced); 2 garlic cloves (minced); 1 tablespoon butter; 1 cup heavy cream (or half-and-half); 1 cup shredded smoked Gouda cheese; ½ cup grated Parmesan cheese; ½ cup breadcrumbs (panko preferred); Salt and pepper (to taste); Optional: fresh thyme (basil, or parsley for garnish)

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Zucchini and yellow squash au gratin is the kind of dish that instantly wraps you in comfort. Creamy, cheesy, golden on top—it’s everything we love about cozy, home-cooked meals. But it also has a fresh, summery soul thanks to its star ingredients: zucchini and yellow squash. These tender veggies are at their peak during the warmer months, making this recipe a perfect seasonal highlight.

What’s beautiful about this gratin is its flexibility. Serve it as a satisfying side dish next to grilled chicken, or let it shine as a meatless main for a light yet indulgent dinner. It’s elegant enough for holiday gatherings and simple enough for casual weeknights.

Whether you’re trying to use up your garden harvest or simply looking for a new way to love your veggies, this au gratin is hearty, wholesome, and guaranteed to please everyone at the table.

What Makes Zucchini and Squash Au Gratin So Irresistible?

“Au gratin” is a French culinary term that refers to a dish baked with a rich topping of cheese, breadcrumbs, or both—until golden and bubbling. It’s the technique that transforms everyday ingredients into something irresistibly decadent.

Traditionally, au gratin dishes begin with a creamy base—often made from milk or cream—and are topped with a layer of cheese that melts and browns in the oven. Sometimes, a breadcrumb topping is added for extra crunch. The result is a beautifully layered texture: creamy underneath, crisp on top.

When applied to vegetables like zucchini and yellow squash, this method enhances their natural sweetness while adding richness and depth. The squash becomes tender and buttery under the heat, absorbing all the savory flavors of garlic, cream, and melted cheese. It’s comfort food elevated by technique—perfectly blending indulgence with wholesome, seasonal ingredients.

Ingredients for Zucchini Squash Casserole (Creamy & Cheesy)

This gratin comes together with simple, fresh ingredients, but each one plays a key role in building flavor and texture.

Zucchini & Yellow Squash: Look for firm, smooth-skinned squash with no soft spots. Medium-sized ones have the best flavor and texture.
Onions & Garlic: Aromatic and essential for depth. Yellow onions work best here for sweetness.
Heavy Cream: This forms the base of the rich sauce. For a lighter option, half-and-half works too.
Parmesan & Smoked Gouda: Parmesan adds sharp, salty notes; Gouda melts beautifully and adds a touch of smoky warmth.
Butter: Used for sautéing and enriching the sauce.
Breadcrumbs: Classic topping that adds a golden crunch. Use panko for extra crispiness.

Tips: Always shred your own cheese—pre-shredded varieties contain anti-caking agents that don’t melt as smoothly. Use a mandoline for perfectly even squash slices, which helps them cook evenly and look beautiful.

Substitutions: For a dairy-free version, try cashew cream or plant-based alternatives. Nutritional yeast can add cheesy flavor for vegan diets. Gluten-free breadcrumbs or crushed almonds also work well as a topping substitute.

Step-by-Step Cooking Instructions

Ready to bring this bubbling beauty to life? Here’s a step-by-step breakdown:

1. Prep the Vegetables:
Wash and dry your zucchini and yellow squash. Slice them into 1/8-inch rounds using a mandoline or sharp knife for even thickness. Lightly salt the slices and let them rest in a colander for 10–15 minutes to draw out moisture. Pat them dry with paper towels.

2. Sauté the Aromatics:
In a skillet over medium heat, melt 1 tablespoon of butter. Add thinly sliced onions and cook until soft and golden, about 8 minutes. Add minced garlic and sauté for another 1–2 minutes until fragrant. Remove from heat.

3. Make the Cream Sauce:
In the same skillet, pour in the heavy cream. Bring it just to a simmer, then stir in half of the shredded Parmesan and smoked Gouda. Stir until melted and smooth. Season with salt, pepper, and a pinch of nutmeg if desired.

4. Assemble the Gratin:
In a greased baking dish, arrange a layer of squash slices slightly overlapping. Add a spoonful of sautéed onions and garlic, then drizzle with cream sauce. Repeat the layers until you’ve used up the ingredients. Top with the remaining cheese and sprinkle with breadcrumbs.

5. Bake:
Preheat your oven to 375°F (190°C). Bake uncovered for 25–30 minutes, or until the top is golden and bubbly. For extra browning, broil for 2–3 minutes at the end—but watch closely!

Pro Tip: Let the gratin rest for 5–10 minutes before serving so the sauce can thicken and set.

What to Serve with Cheesy Zucchini Squash Gratin

Zucchini and yellow squash au gratin is a flexible dish that pairs beautifully with a variety of meals. Serve it alongside grilled steak, roasted chicken, or even as a creamy side at your next holiday dinner.

If you’re going meatless, serve it as the main event with a fresh green salad and crusty bread. Want to impress guests? Garnish the top with freshly chopped herbs like parsley, thyme, or basil for a burst of color and brightness.

You can even make mini gratins in ramekins for a charming individual presentation—perfect for brunches or dinner parties.

How to Store and Reheat Zucchini Gratin Leftovers

Leftovers? No problem. Let the gratin cool completely, then store it in an airtight container in the fridge for up to 4 days.

To reheat, place portions in a preheated oven at 350°F (175°C) for 10–15 minutes until warmed through. Avoid microwaving if you want to preserve the crispy topping—it tends to get soggy.

This dish can also be made a day in advance. Assemble everything, cover tightly, and refrigerate. Bake when ready to serve. You may need to add a few extra minutes to the baking time if starting from cold.

Zucchini and Squash Gratin Recipe Variations to Try

One of the best parts about zucchini and yellow squash au gratin is how flexible it is. With a few thoughtful tweaks, you can tailor this dish to suit your pantry, diet, or flavor preferences.

Cheese Alternatives:
Not a fan of Gouda? Try sharp cheddar for bold flavor, Gruyère for a nutty French twist, or mozzarella for that classic gooey pull. You can even mix cheeses for a more complex flavor—just make sure they melt well.

Additional Vegetables:
This gratin is the perfect vehicle for extra produce. Thin slices of Yukon Gold potatoes add hearty richness. Tomato slices bring bright acidity and pair beautifully with herbs. Bell peppers offer sweetness and color—just sauté them slightly before layering.

Herb Infusions:
Fresh herbs elevate the dish with aroma and brightness. Thyme adds earthiness, basil gives a sweet, peppery note, and rosemary pairs well with creamy, cheesy layers. Sprinkle herbs between layers or mix into your sauce for full infusion.

Dietary Modifications:

Vegan: Use unsweetened plant-based cream (like oat or cashew) and your favorite dairy-free cheese. Top with seasoned breadcrumbs mixed with olive oil.
Gluten-Free: Use almond flour or gluten-free breadcrumbs. Make sure your cheese and cream are certified GF if needed.

No matter how you spin it, this gratin welcomes creativity while keeping its cozy soul intact.

Expert Tips for Success

To make a truly standout gratin, a few small techniques go a long way:

Slice evenly:
Use a mandoline or a sharp knife to get thin, consistent slices. This helps everything cook at the same rate and gives the dish that elegant layered look.

Salt and drain the squash:
Zucchini and yellow squash hold a lot of water, which can turn your gratin soggy. After slicing, sprinkle them with salt and let them sit for 10–15 minutes. Then, blot with paper towels to remove excess moisture.

Choose quality cheeses:
Freshly shredded cheese melts more smoothly and tastes better than pre-shredded varieties. Go for cheeses that complement each other in flavor and texture—like sharp Parmesan with a mellow melting cheese like Gouda or Gruyère.

Don’t overbake:
You want a golden crust, not a dried-out base. Bake just until bubbly and browned on top—around 25–30 minutes. If needed, broil briefly to crisp the top without overcooking the inside.

Pro Tip: Let it rest 5–10 minutes after baking so the sauce thickens and slices hold their shape beautifully on the plate.

FAQs About Baked Zucchini and Yellow Squash Au Gratin

Can I prepare this dish ahead of time?
Absolutely! You can slice and layer everything, add the sauce and cheese, then cover and refrigerate. Bake it fresh when you’re ready to serve. Just add a few extra minutes to the bake time if it’s coming straight from the fridge.

How do I prevent a watery gratin?
This is the #1 question—and the answer is all about prepping your veggies. Salt the zucchini and squash slices and let them sit in a colander for 10–15 minutes. Pat them dry before layering. This helps release excess moisture and keeps your gratin creamy, not soggy.

Can I freeze leftovers?
Technically, yes. But the texture of the squash may change a bit after thawing. If you do freeze it, reheat in the oven rather than the microwave for best results. Still, this dish is definitely at its best when enjoyed fresh or stored in the fridge for 2–3 days.

What are the best cheeses for this recipe?
We love using Parmesan, smoked Gouda, and Gruyère—each adds a different layer of flavor. For something simpler, try mozzarella and cheddar. Just be sure your cheese melts well and balances sharpness with creaminess.

Is it necessary to peel the squash?
Nope! The skins are perfectly edible, add a touch of texture, and help the slices hold their shape while baking. Just give them a good wash and slice away.

Conclusion: Embracing Seasonal Cooking

Zucchini and yellow squash au gratin is more than just a side dish—it’s a celebration of seasonal produce, comfort food, and creativity in the kitchen. Whether you’re using up garden zucchini or adding a touch of elegance to your dinner table, this gratin adapts beautifully to your mood, your pantry, and your guests.

Don’t be afraid to mix in your favorite herbs, experiment with new cheeses, or sneak in extra veggies. Cooking is about making a dish your own. We’d love to hear how you made it—share your twist on this classic gratin in the comments!