Growing up in an Italian-American family, squash was a staple in our kitchen. Every summer, my grandmother’s backyard garden would overflow with vibrant zucchinis and sun-kissed yellow squash. She would cook them simply — grilled with olive oil or stewed in a hearty tomato sauce. But one rainy afternoon, she surprised us with something different: a bubbling, golden-brown Zucchini and Yellow Squash Au Gratin.
It was rich, creamy, and comfortingly cheesy, a dish that felt like a hug on a plate. Today, I’m sharing a version of her classic, updated to be perfect for any season!
Table of Contents
Why You’ll Love This Zucchini and Yellow Squash Au Gratin
- Versatile: Great as a side dish or a main course.
- Seasonless: Delicious with winter squash or fresh summer harvest.
- Easy to Make: Simple ingredients and a foolproof method.
- Family Favorite: Kid-approved and a crowd-pleaser at potlucks.
Ingredients You’ll Need
Here’s what you’ll gather for this hearty dish:
- 3 medium zucchinis (sliced into ¼-inch rounds)
- 3 medium yellow squash (sliced into ¼-inch rounds)
- 2 tablespoons olive oil
- 1 small yellow onion (finely diced)
- 2 cloves garlic (minced)
- 1 cup heavy cream
- 1 cup shredded sharp cheddar cheese
- 1 cup shredded Gruyère cheese
- ½ cup grated Parmesan cheese
- ¾ cup panko breadcrumbs
- 2 tablespoons butter (melted)
- ½ teaspoon dried thyme
- ½ teaspoon dried oregano
- ½ teaspoon salt
- ¼ teaspoon black pepper
- ¼ teaspoon nutmeg (optional, for warmth)
- Fresh parsley (for garnish)
Step-by-Step Instructions
1. Prep the Vegetables
- Preheat your oven to 375°F (190°C).
- Lightly grease a 9×13-inch baking dish with olive oil or butter.
- Slice your zucchinis and yellow squash evenly so they cook at the same rate.
2. Sauté the Aromatics
- In a large skillet over medium heat, add olive oil.
- Sauté the onion until translucent, about 5 minutes.
- Stir in the garlic and cook for another minute, releasing that irresistible aroma.
3. Layer the Squash
- Arrange half of the zucchini and squash slices in the baking dish.
- Sprinkle with a pinch of salt, pepper, thyme, and oregano.
4. Make the Creamy Sauce
- In the same skillet, pour in the heavy cream and bring it to a gentle simmer.
- Stir in half of the cheddar, Gruyère, and Parmesan cheeses until melted and smooth.
- Season with a touch of nutmeg for extra coziness if desired.
5. Assemble the Gratin
- Pour half the cream sauce over the first layer of squash.
- Repeat with the remaining squash slices and top with the rest of the sauce.
6. Add the Crunchy Topping
- In a small bowl, combine panko breadcrumbs, melted butter, and the remaining Parmesan cheese.
- Sprinkle evenly over the top for that signature golden crust.
7. Bake to Perfection
- Bake uncovered for 30-35 minutes, or until the top is bubbly and golden brown.
- Let it cool slightly before serving — the sauce thickens as it rests!
8. Garnish and Serve
- Sprinkle with fresh parsley for a pop of color and freshness.
Tips for Success
- Use a mandoline slicer for perfectly even vegetable slices.
- Salt the squash lightly and let them sit for 15 minutes to draw out excess water if you want an extra-thick gratin.
- Swap cheeses — try mozzarella for extra stretchiness or fontina for a mild melt.
Variations You’ll Adore
- Low-Carb Version: Use heavy cream and skip the breadcrumbs.
- Add Protein: Mix in cooked chicken or crumbled sausage.
- Make It Vegan: Substitute cashew cream and vegan cheeses, and use a dairy-free butter for the topping.
What to Serve with Zucchini and Yellow Squash Au Gratin
Pair this dish with:
- Grilled meats like steak or chicken
- Fresh garden salads with a zesty vinaigrette
- Warm crusty bread for sopping up that creamy sauce
Quick and Easy Zucchini and Yellow Squash Au Gratin
- Total Time: 55 minutes
- Yield: 6–8 servings 1x
Description
A creamy, cheesy Zucchini and Yellow Squash Au Gratin that’s rich and comforting yet light enough for any season. This American classic side dish (or main!) is perfect for family dinners, holiday gatherings, or cozy weeknight meals.
Ingredients
Scale
- 3 medium zucchinis, sliced into ¼-inch rounds
- 3 medium yellow squash, sliced into ¼-inch rounds
- 2 tablespoons olive oil
- 1 small yellow onion, finely diced
- 2 cloves garlic, minced
- 1 cup heavy cream
- 1 cup shredded sharp cheddar cheese
- 1 cup shredded Gruyère cheese
- ½ cup grated Parmesan cheese
- ¾ cup panko breadcrumbs
- 2 tablespoons butter, melted
- ½ teaspoon dried thyme
- ½ teaspoon dried oregano
- ½ teaspoon salt
- ¼ teaspoon black pepper
- ¼ teaspoon nutmeg (optional)
- Fresh parsley, for garnish
Instructions
- Preheat and Prepare:
Preheat the oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish with olive oil or butter. - 2. Slice the Squash:
Slice the zucchini and yellow squash into ¼-inch thick rounds for even cooking. - 3. Sauté Onion and Garlic:
Heat olive oil in a skillet over medium heat. Add diced onion and sauté until translucent, about 5 minutes. Add minced garlic and cook for 1 minute. - 4. Layer the Vegetables:
Arrange half the zucchini and squash slices in the baking dish. Season with salt, pepper, thyme, and oregano. - 5. Make the Cheese Sauce:
In the same skillet, add the heavy cream and bring it to a simmer. Stir in half of the cheddar, Gruyère, and Parmesan until melted and smooth. Add a pinch of nutmeg if using. - 6. Assemble the Gratin:
Pour half of the cheese sauce over the first layer of squash. Add the remaining squash slices and pour the rest of the sauce on top. - 7. Prepare the Topping:
Mix the panko breadcrumbs with melted butter and the remaining Parmesan cheese. Sprinkle evenly over the dish. - 8. Bake:
Bake uncovered for 30-35 minutes, until golden and bubbly. Let cool slightly before serving. - 9. Garnish and Serve:
Sprinkle with chopped fresh parsley and serve warm.
Notes
- For a thicker gratin, lightly salt the squash slices and let them drain for 15 minutes before layering.
- Swap cheeses if desired: mozzarella, fontina, or gouda work beautifully.
- You can prepare the dish a day ahead and refrigerate it before baking.
- Prep Time: 20 minutes
- Cook Time: 35 minutes
- Category: Dinner
- Cuisine: American
Keywords: Zucchini and Yellow Squash Au Gratin, easy squash gratin, cheesy vegetable casserole, summer squash recipe, baked zucchini
Storage and Reheating
- Store: Leftovers can be kept in an airtight container in the fridge for up to 3 days.
- Reheat: Bake at 350°F (175°C) for 10-15 minutes, or microwave gently until heated through.
Frequently Asked Questions
Can I freeze the au gratin?
While technically possible, the texture of the squash may become watery when thawed. It’s best enjoyed fresh.
Can I make it ahead?
Absolutely! Assemble the dish (without baking), cover it tightly, and refrigerate for up to 24 hours before baking.
Can I add potatoes?
Sure! Layer in thin slices of Yukon Gold potatoes for a heartier version.
