Summer Squash Gratin

Let your summer produce shine in this delicious gratin recipe.

Summer Squash Gratin
Photo: Antonis Achilleos; Food Styling: Emily Nabors Hall; Prop Styling: Heather Chadduck Hillegas
Active Time:
30 mins
Total Time:
30 mins

This summer, vegetables are looking better than ever—especially when they come in the form of a pretty gratin. In this Summer Squash Gratin, fresh vegetables play the starring role. Usually, you'll find a squash casserole anchored by a mixture of sour cream, mayonnaise, and a blend of cheeses. This version of squash gratin forgoes all the creamy bells and whistles, allowing the flavor of the squash to really shine. This recipe spotlights a mix of yellow squash and zucchini, cooked simply with sweet onion, garlic, and thyme, and tops it off with buttery, cheesy breadcrumbs that crisp under the broiler. The panko topping is really the finishing touch that brings a crunch factor to this vegetable side.

After a quick sauté, the squash stays crisp-tender and, unlike in some other squash casseroles, does not get soggy. We cover the skillet for the first half of the cooking time to helps the squash to cook down quickly; uncovering for the latter half helps any accumulated liquid evaporate.


  • 3 garlic cloves

  • 4 tablespoons unsalted butter, divided

  • 1 ½ cups thinly sliced Vidalia onion (from 1 small onion)

  • 1 pound yellow squash, sliced ¼ inch thick (about 4 cups)

  • 1 pound zucchini, sliced ¼ inch thick (about 4 cups)

  • 2 teaspoons chopped fresh thyme

  • ½ teaspoon black pepper

  • 1 teaspoon kosher salt, divided

  • ½ cup panko breadcrumbs

  • 2 ounces Parmesan cheese, grated (about ½ cup)


  1. Preheat oven to broil with rack 6 inches from heat source. Mince 2 of the garlic cloves, and set aside. Grate remaining garlic clove; set aside separately.

  2. Melt 2 tablespoons of the butter in a 10-inch cast-iron skillet over medium. Add onion. Cook, stirring occasionally, until starting to soften, about 3 minutes. Stir in squash, zucchini, thyme, and reserved minced garlic. Increase heat to medium-high. Cover and cook until mixture starts to soften, about 6 minutes, stirring once halfway through cook time. Uncover and cook, stirring occasionally, until mixture is tender, about 6 minutes. Stir in pepper and ¾ teaspoon of the salt. Remove from heat.

  3. Microwave remaining 2 tablespoons butter in a small microwavable bowl on HIGH until melted, about 30 seconds. Add panko, cheese, reserved grated garlic, and remaining ¼ teaspoon salt; stir together until combined. Sprinkle evenly over squash mixture. Broil in preheated oven until topping is browned and crisp, 1 to 2 minutes.

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