Zucchini Gratin

Close up of a square removed from the corner of a gratin in a baking dish.

This recipe for zucchini gratin features summer squash and onions in a creamy sauce topped with crispy, buttery breadcrumbs. It tastes light and rich at the same time with a delicate, mouthwatering flavor.

5 from 4 votes

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Course: Side Dish

Cuisine: American

Keyword: gruyere, nutmeg, zucchini gratin

Prep Time: 10

Cook Time: 40

Total Time: 50

Servings: servings

Calories: 238kcal

Author: Nicole Gaffney (ColeyCooks.com)

Ingredients

4 tablespoons unsalted butter divided, plus more for buttering the baking dish
½ lb yellow onions about 2 medium cut in half and sliced
1 lb zucchini 2 medium or 1 extra large, sliced ¼ inch thick
1 teaspoon salt
½ teaspoon freshly ground black pepper
⅛ teaspoon freshly grated nutmeg
2 tablespoons flour
½ cup whole milk
¾ cup panko or fresh bread crumbs
¾ cup grated Gruyere cheese
Minced fresh parsley or chives to garnish optional

Instructions

Preheat the oven to 400 degrees.
Butter a small, shallow baking dish, about 7" x 10", or a 9-inch cast iron skillet and set aside.
Melt 3 tablespoons of butter in a large sauté pan over medium heat. Add the onions and cook for about 6-8 minutes, stirring occasionally, until they are softened but not browned.
Add the zucchini, toss around, then cover and cook for about 8 minutes until softened.
Add the salt, pepper and nutmeg, then sprinkle the flour over top and mix.
Add the milk, stir and continue cooking until the mixture has thickened, about 3-4 minutes.
Pour the zucchini mixture into the prepared baking dish.
Combine the breadcrumbs with the Gruyere cheese and sprinkle over the zucchini, then dot the remaining tablespoon of butter evenly over the top.
Bake for about 20 minutes or until the top is golden brown and bubbling.
Sprinkle chopped parsley or chives over the top to garnish, if desired. Allow to cool at least 10 minutes before serving.

Notes

If using very large zucchini from the garden, they can sometimes have tough skin and large, hard seeds. In this case, it's best to peel and remove the seeds with a spoon before slicing.
For a richer, more decadent zucchini gratin, swap out the milk for heavy cream and double the cheese.
If baking in a convection oven, lower the heat to 375 degrees F or the top could brown too quickly.
If the top of the gratin isn't browned enough by the time it's finished baking, pop it under the broiler for a minute or two. Watch it carefully so it doesn't burn.

Nutrition