Go Back

Zucchini Gratin with Yellow Squash

Zucchini gratin with yellow squash layered in overlapping rows and baked until creamy and golden with a bubbling gruyère crust. This French-style summer vegetable gratin bakes with a breadcrumb topping for crackly edges.
Print Recipe Pin Recipe
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 zucchini thinly sliced
  • 2 yellow squash thinly sliced
  • 1 onion thinly sliced
  • 3 garlic minced
  • 1 tsp fresh thyme
dairy and seasoning
  • 2 tbsp butter for sautéing
  • 1 cup heavy cream
  • 0.5 cup chicken or vegetable broth
  • 0.5 tsp salt to taste
  • 0.25 tsp 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 butter over medium heat for 4 minutes.
  2. Add the garlic and thyme and cook for 30 seconds.
Assemble the gratin
  1. Layer the zucchini and yellow squash slices in the baking dish in overlapping rows, alternating colors.
  2. Scatter the sautéed onion and garlic over the top.
  3. Whisk the heavy cream, broth, salt, and black pepper, then pour over the vegetables.
  4. Sprinkle 3/4 cup of gruyère or Swiss cheese over the top.
  5. Mix the remaining gruyère or Swiss cheese, parmesan, and panko breadcrumbs with melted butter, then scatter over everything.
Bake
  1. Cover with foil and bake at 375°F for 25 minutes.
  2. Uncover and bake for 15–20 minutes at 375°F until golden and bubbling, with a crackly breadcrumb-cheese surface.

Notes

For the creamiest texture, slice the zucchini and yellow squash thinly and evenly so they cook at the same rate; aim for a similar thickness across the whole dish. Store leftovers covered in the refrigerator up to 3–4 days. This gratin also freezes well up to 2 months; thaw overnight in the fridge and reheat until hot and bubbling. Dietary swap: use half-and-half or a lactose-reduced cream plus lactose-reduced cheese to reduce dairy lactose while keeping the same gratin bake.