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Easy Make-Ahead Zucchini Gratin
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4.54 from 15 votes

Easy Make Ahead Zucchini Gratin

A gratin is a dish topped with a golden browned crust of breadcrumbs and/or melted cheese. In France, gratins are generally made with potatoes. This Easy Make Ahead Zucchini Gratin is an amazing deviation which will have you coming back for more!
Prep Time40 mins
Cook Time20 mins
Total Time1 hr
Course: Side Dish
Cuisine: American
Servings: 4 servings
Calories: 247kcal
Author: Chula King


  • ½ cup (2 ounces) grated Gruyère cheese (See Tip 1)
  • ½ cup (1.5 ounces) Panko breadcrumbs (See Tip 2)
  • 2 large zucchini, about 1 pound total
  • 1 large onion (between 8 and 9 ounces)
  • 1 teaspoon Kosher salt, divided
  • 4 Tablespoons butter, divided
  • 1 ½ Tablespoons all-purpose flour
  • ¾ cup (6-ounces) milk
  • ¼ teaspoon freshly ground black pepper
  • teaspoon freshly ground nutmeg (See Tip 3)


  • Preheat oven to 400° F. Spray a casserole dish with nonstick spray. Set aside.
  • Combine Gruyère and Panko breadcrumbs in a bowl; set aside.
  • Scrub zucchini under cold water; cut off the two ends, but do not peel. Cut off two ends of onion, and peel. Grate the zucchini and onion in food processor of box grater; toss with ½ teaspoon salt in a colander. Let sit for 30 minutes.
  • Squeeze liquid from zucchini and onion with hands. Then place in double paper towel and continue squeezing as much liquid as possible. (See Tip 4)
  • Heat 3 tablespoons of the butter to foaming over medium heat in a 12-inch nonstick skillet. Add the grated zucchini and onion. Cook for 3 to 5 minutes, just until tender. Season with remaining ½ teaspoon of salt, pepper nutmeg. Add flour; stir well to combine and cook for a minute or two.
  • Add milk; stir constantly until thickened and bubbly. Correct seasonings.
  • Transfer zucchini mixture to prepared casserole dish. Top with Gruyère/Panko mixture. Dot with remaining tablespoon of butter. Can be made ahead of time up to this point. (See Tip 5)
  • Bake in a preheated 400º F oven for 20 minutes or until bubbling hot and golden browned. Yield: 4 servings. (See Tip 6)


  1. May substitute Swiss cheese, Cheddar cheese, Monterey Jack cheese or Fontina cheese for the Gruyère cheese.
  2. May use plain breadcrumbs in place of the Panko.
  3. May use store-bought ground nutmeg in place of the freshly ground nutmeg.
  4. You'll be surprised at the amount of liquid that you can squeeze from the zucchini and onion! The reserved liquid from the zucchini and onion can be used in sauces or gravies.
  5. If made ahead of time, cover and refrigerate for up to a day. Add 5 minutes to the baking time
  6. Leftovers, if any, can be reheated in a 350°F oven for 10 to 15 minutes. They can also be reheated in the microwave for several minutes. However, if reheated in the microwave, the cheese toping will lose its crispiness.


Calories: 247kcal | Carbohydrates: 16g | Protein: 7g | Fat: 17g | Saturated Fat: 10g | Cholesterol: 47mg | Sodium: 790mg | Potassium: 381mg | Fiber: 1g | Sugar: 6g | Vitamin A: 730IU | Vitamin C: 19.6mg | Calcium: 198mg | Iron: 0.9mg