Creamy Zucchini Gratin with Lemony Breadcrumbs

Kelli Foster
Kelli FosterCulinary Producer at The Kitchn
I'm a recipe developer, food writer, stylist, and video producer, with more than 10 years of professional experience. As an expert meal planner and avid home cook who loves grocery shopping and helping people figure out what to cook for dinner, I'm a natural fit as The Kitchn’s Dinner Therapist. Since graduating from The University of Scranton and The French Culinary Institute, I've authored three cookbooks: Buddha Bowls, Plant-Based Buddha Bowls, and The Probiotic Kitchen. My kitchen superpower is turning a random assortment of ingredients into easy, delicious dinners that even my young son will eat.
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published Jul 20, 2022
summer
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Credit: Kelli Foster

Serves6

Prep10 minutes

Cook33 minutes to 38 minutes

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Credit: Kelli Foster

I have a long list of zucchini recipes I want to make throughout summer, but the one I’m most excited about is this comforting zucchini gratin. While a creamy, cheesy casserole sounds like a side that might be a little too rich for hot summer days, this version includes a bright, fresh twist that keeps it in check for the season: a crisp, buttery breadcrumb topping spiked with lemon zest for a bright and summery pop of flavor to contrast the creamy Gruyère sauce.

What Ingredients Are in Zucchini Gratin?

The main ingredient is, of course, zucchini. The recipe calls for two pounds, and I recommend using small (you’ll need about eight) or no larger than medium (you’ll need about four) zucchini, which are sweet, mellow, and less watery than their larger counterparts.

  • Zucchini
  • Shallots
  • Garlic
  • Gruyère cheese
  • Parmesan cheese
  • Lemon
  • Panko breadcrumbs
  • Unsalted butter
  • All-purpose flour
  • Whole or 2% milk
Credit: Kelli Foster

How Do You Make Zucchini Casserole?

Here’s how to make creamy zucchini casserole.

  1. Prepare the breadcrumb topping. Mix a combo of panko, grated Parm, lemon zest, melted butter, and a pinch of salt.
  2. Make the sauce. After sautéing shallot and garlic, make a basic béchamel sauce, then stir in a handful of grated Gruyère.
  3. Mix in zucchini. Once the cheese is melted, remove the pot from the heat, add the sliced zucchini, and stir well until the rounds are totally coated. Be sure to separate any zucchini rounds that stick together.
  4. Layer in baking dish. Transfer the zucchini mixture and sauce to the baking dish. Sprinkle the breadcrumb topping in an even layer of the zucchini.
  5. Bake. Cook the gratin until the sauce is bubbling and the breadcrumbs are golden-brown.

Can I Freeze Zucchini Gratin?

No. Because of the vegetable’s high water content, zucchini gratin doesn’t thaw well after being frozen. The gratin is at its best the day it’s baked, although leftovers will keep well in an airtight container stored in the fridge for up to four days.

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Zucchini Gratin Recipe

Prep time 10 minutes

Cook time 33 minutes to 38 minutes

Serves 6

Nutritional Info

Ingredients

  • Cooking spray

  • 2 pounds

    zucchini (about 4 medium or 8 small)

  • 2 medium

    shallots

  • 2 cloves

    garlic

  • 4 ounces

    Gruyere cheese

  • 1 medium

    lemon

  • 3/4 cup

    panko bread crumbs

  • 2 tablespoons

    grated Parmesan cheese

  • 1 1/2 teaspoons

    kosher salt, divided

  • 6 tablespoons

    unsalted butter

  • 3 tablespoons

    all-purpose flour

  • 1 1/4 cups

    whole or 2% milk

  • 1/4 teaspoon

    freshly ground black pepper

  • 1/4 teaspoon

    freshly grated nutmeg

Instructions

  1. Arrange a rack in the middle of the oven and heat the oven to 400°F. Coat an 8- or 9-inch square or other 2-quart baking dish with cooking spray or butter.

  2. Trim the ends from 2 pounds zucchini and cut crosswise into 1/4-inch thick rounds. Thinly slice 2 shallots. Mince 2 garlic cloves. Grate 4 ounces Gruyere cheese (about 1 1/2 cups) on the large holes of a box grater. Finely grate the zest of 1 medium lemon into a medium bowl; reserve the lemon for another use.

  3. Add 3/4 cup panko bread crumbs, 2 tablespoons grated Parmesan cheese, and 1/4 teaspoon of the kosher salt into the bowl of lemon zest. Stir to combine.

  4. Melt 6 tablespoons unsalted butter in a Dutch oven or large pot over medium heat. Transfer 2 tablespoons into the breadcrumb mixture. Stir to coat the breadcrumbs.

  5. Add the shallot, garlic, and 1/4 teaspoon of the kosher salt to the remaining butter in the Dutch oven and cook over medium heat, stirring occasionally, until softened, 2 to 3 minutes. Sprinkle with 3 tablespoons all-purpose flour and stir constantly for 1 minute to cook out the floury taste. While stirring constantly, slowly pour in 1 1/4 cups whole or 2% milk and stir until no lumps remain and the flour is completely dissolved. Bring just to a full simmer over medium heat, stirring frequently.

  6. Add the Gruyère, the remaining 1 teaspoon kosher salt, 1/4 teaspoon black pepper, and 1/4 teaspoon grated nutmeg, and stir until the cheese is melted and the sauce is bubbling. The sauce will be thick and will thin out during baking. Remove the pot from the heat.

  7. Add the zucchini and stir to coat, making sure to separate any stuck together slices. Transfer to the prepared baking dish and spread in an even layer.

  8. Sprinkle the gratin with the breadcrumb mixture.

  9. Bake until the gratin is golden-brown on top and bubbling around the edges, 28 to 30 minutes. Let cool for 5 minutes before serving.

Recipe Notes

Storage: Leftovers can be refrigerated in an airtight container for up to 4 days.

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Ingredient
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milk
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pantry
Vegetables