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Zucchini Gratin with Yellow Squash

Zucchini gratin with yellow squash layers thin-sliced summer vegetables in a creamy, golden bake. Topped with a bubbling gruyère-and-breadcrumb crust, it’s a classic French squash gratin style side dish.
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Prep Time 20 minutes
Cook Time 45 minutes
Total Time 1 hour 5 minutes
Servings: 6 servings
Course: Side Dish
Cuisine: French-American
Calories: 420
Ingredients Equipment Method Notes

Ingredients
  

Vegetables
  • 2 medium zucchini thinly sliced
  • 2 medium yellow squash thinly sliced
  • 1 small onion thinly sliced
  • 3 garlic cloves minced
Cream mixture
  • 2 tbsp butter
  • 1 cup heavy cream
  • 0.5 cup chicken or vegetable broth
  • 1 tsp fresh thyme
  • 0.1 salt to taste
  • 0.1 black pepper to taste
Cheese and topping
  • 1 cup gruyère or Swiss cheese shredded (divided)
  • 0.25 cup parmesan grated
  • 0.33 cup panko breadcrumbs
  • 2 tbsp butter melted (for topping)

Equipment

  • 1 sheet pan

Method
 

Prep and preheat
  1. Preheat the oven to 375°F and grease a 9x13 baking dish.
Sauté aromatics
  1. Sauté the onion in the butter over medium heat for 4 minutes, until softened.
  2. Add the garlic and fresh thyme and cook for 30 seconds, just until fragrant, then remove from heat.
Layer vegetables
  1. Layer the zucchini and yellow squash slices in the baking dish in overlapping rows, alternating colors.
  2. Scatter the sautéed onion and garlic evenly over the top.
Assemble gratin and bake
  1. Whisk the heavy cream, broth, salt, and black pepper, then pour evenly over the vegetables.
  2. Sprinkle 3/4 cup of the shredded gruyère over the top.
  3. Mix the remaining gruyère, parmesan, and panko with the melted butter, then scatter over everything.
  4. Cover with foil and bake for 25 minutes at 375°F, until the vegetables are tender and bubbling around the edges.
  5. Uncover and bake 15–20 more minutes at 375°F until golden and bubbling.

Notes

For the creamiest texture, slice zucchini and yellow squash evenly so the layers cook at the same rate. Refrigerate covered up to 3 days; reheat in a 350°F oven until hot and re-bubbling (about 15–20 minutes). Freezing is not recommended because the squash can soften and release extra moisture after thawing. For a dairy-light swap, use half-and-half for the heavy cream (flavor will be milder, and the top may brown slightly less).