Zucchini Gratin With Cheddar Cheese

zucchini gratin

The Spruce / Diana Rattray

Prep: 15 mins
Cook: 35 mins
Total: 50 mins
Servings: 6 servings
Nutrition Facts (per serving)
352 Calories
24g Fat
26g Carbs
11g Protein
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Nutrition Facts
Servings: 6
Amount per serving
Calories 352
% Daily Value*
Total Fat 24g 31%
Saturated Fat 14g 69%
Cholesterol 61mg 20%
Sodium 492mg 21%
Total Carbohydrate 26g 9%
Dietary Fiber 3g 12%
Total Sugars 8g
Protein 11g
Vitamin C 28mg 141%
Calcium 267mg 21%
Iron 2mg 11%
Potassium 714mg 15%
*The % Daily Value (DV) tells you how much a nutrient in a food serving contributes to a daily diet. 2,000 calories a day is used for general nutrition advice.
(Nutrition information is calculated using an ingredient database and should be considered an estimate.)

This zucchini gratin is a flavorful side dish casserole with extra richness from the cheddar cheese. A gratin is a baked dish with a creamy sauce and crunchy topping, and is always a nice way to make a fancy side dish out of everyday vegetables. If you or your neighbors have an abundance of garden-fresh summer squash or zucchini, this is an excellent way to use it.

The casserole is a good choice for a holiday meal or Sunday dinner, and it is a nice low-carb replacement for scalloped potatoes or mashed potatoes.


  • 8 tablespoons (4 ounces) unsalted butter, divided

  • 1 large onion, chopped

  • 2 pounds zucchini, sliced (about 6 cups)

  • 2 tablespoons all-purpose flour

  • 1 cup milk

  • 1 teaspoon kosher salt, or to taste

  • 1/4 teaspoon mustard powder

  • Freshly ground black pepper, to taste

  • 1 pinch nutmeg, optional

  • 1 cup shredded cheddar cheese

  • 4 slices bacon, cooked until crisp, drained, crumbled, optional

  • 1 cup soft, fresh breadcrumbs

Steps to Make It

  1. Gather the ingredients.

  2. Preheat the oven to 350 F. Butter a 1 1/2-quart baking dish.

  3. In a large skillet over medium heat, melt 4 tablespoons of the butter. Add the chopped onion and sauté, stirring, until it is tender and translucent.

  4. Add the sliced zucchini to the skillet and reduce the heat to low. Cover the pan and cook for 10 to 15 minutes, or just until tender. Remove the vegetables to a bowl with a slotted spoon and set aside.

  5. Add 2 tablespoons of the butter to the skillet and melt over medium-low heat. Add the flour and cook, stirring constantly, for 2 minutes.

  6. Gradually add the milk to the flour and butter roux and continue cooking until thickened, stirring constantly. Add the kosher salt, mustard powder, and black pepper, along with a dash of nutmeg, if desired. Taste the sauce and adjust the seasonings, as needed.

  7. There will be some excess liquid from the cooked zucchini, so use a slotted spoon to transfer the zucchini and onion back to the skillet. Stir the mixture gently to coat the zucchini with the sauce. 

  8. Turn the zucchini and sauce mixture into the prepared baking dish. Sprinkle the shredded cheese over the casserole along with the cooked crumbled bacon, if using.

  9. Melt the remaining 2 tablespoons of butter and toss with the breadcrumbs. Sprinkle over the zucchini casserole.

  10. Bake the gratin in the preheated oven for 20 to 25 minutes, or until the topping is browned and the casserole is bubbling around the edges.

Recipe Variations

  • You can use any type of summer squash in this recipe. While zucchini and yellow squash are very similar, yellow squash tends to be a bit sweeter.
  • Make it with or without the crumbled cooked bacon or add even more richness with half-in-half or light cream instead of the milk.
  • For a touch of garlic flavor, add about 1 teaspoon of finely chopped garlic to the skillet along with the zucchini.
  • For the topping, instead of all cheddar, feel free to use a combination of cheddar and mozzarella cheese or another kind of melting cheese.

Do you peel summer squash?

The peel for zucchini and other summer squashes is thin and tender, especially when cooked. There is no need to peel the veggies, especially since this is where much of the nutritional value is stored.