squash casserole in a cast iron skillet on a table loaded with food

Cheesy Squash Casserole.

  • Author: Bet Denton
  • Prep Time: 7
  • Cook Time: 53
  • Total Time: 1 hour
  • Yield: 8 servings


  • 4 tablespoons butter
  • 2 large onions, sliced
  • 6 medium yellow squash, sliced (or zucchini, or a combination – frozen is fine!)
  • kosher salt and pepper
  • 1/4 teaspoon nutmeg
  • 3 tablespoons all-purpose flour
  • 1-1/3 cups milk, warmed (I used 1%, but use whatever you have on hand)
  • 1-1/2 cups fresh breadcrumbs (or about half that amount of regular dry breadcrumbs or panko)
  • 1-1/2 cups freshly grated cheese (cheddar, Gruyere, asiago – use your favorite or a combination!)
  • a drizzle of olive oil (or more butter)


  1. Preheat the oven to 400. Melt the butter in a 12-inch cast iron skillet (or other large ovenproof skillet, if you plan on baking in the pan) and sauté the onions for 5-10 minutes on medium-low to medium heat to soften.
  2. Add the sliced squash and season with salt, pepper, and nutmeg. Cook for 15-20 minutes (if using frozen, partially cooked squash, this may take less time), until cooked down (the liquid they release will have mostly evaporated).
  3. Sprinkle with flour and stir to cook for 1 minute. Add milk and stir, letting the mixture thicken over low heat for 2-3 minutes.
  4. To cook in the skillet, sprinkle with combined breadcrumbs and cheese, or transfer to a large baking dish (9×13 or bigger) before topping. Drizzle with oil or dot with bits of butter, and bake for 20 minutes until the topping is brown and crispy and beautiful!


Adapted from Ina Garten’s Zucchini Gratin