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Zucchini and Squash Gratin

I didn’t grow up eating very many “gratins.” There were certain things that just weren’t in our usual repertoire, and there is nothing wrong with that – my mother knew what worked for her very particular children, and we stuck with it.

Spiralized Zucchini and Squash

Oh how times change. Now, I eat just about everything, and I now live close enough to my mom where we can try things that never really existed in our recipe box before. I still had the last of the zucchini and squash from our garden, and was ready to make a comforting, fall side dish.

Spiralized Onions

We were looking at zucchini gratin recipes and knew we wanted to combine it with the squash. However, this dish would be great with zucchini only, if that was all that you had. Most recipes have you cook the zucchini on the stove and then pour it into a baking dish to go into the oven – my mom looked at me and said, “how about we just do it all in a cast iron skillet?” Um, yes to one pot wonders.

grating nutmeg into the veggies

On a whim, we decided to use my spiralizer to cut the veggies into super thin ribbons (which were kind of like slices). This cuts down your cooking time since they are so thin they cook pretty fast – but slicing them thin with a knife or mandolin would work great too. Once spiralized, cooked, covered in cheese and breadcrumbs, then baked…you barely you know you are eating vegetables. I’m ok with this.

Zucchini and Squash Gratin

Zucchini and Squash Gratin
by Lauren & Lulu
Serves 6


  • 2 tablespoons unsalted butter, plus extra for topping
  • 1 large yellow onion, cut in 1/2 and sliced (or spiralized!)
  • 2 cloves garlic, minced
  • 1 pound zucchini, spiralized (we used one very large zucchini from our garden – 2 smaller store bought ones would also work. If you don’t have a spiralizer slice 1/4 inch thick or smaller)
  • 1 pound yellow summer squash, spiralized (we used 1 large straightneck from our garden, if you don’t have a spiralizer slice as thin as you can)
  • 2 teaspoons kosher salt
  • 1 teaspoon freshly ground black pepper
  • 1/4 teaspoon ground nutmeg
  • 1 tsp herbes de provence
  • 2 tablespoons all-purpose flour
  • 1 cup warm milk or cream (we used half and half)
  • 1/4 cup panko
  • 1/2 cup bread crumbs
  • 3/4 cup grated Gruyere


Preheat the oven to 400 degrees F.

Melt the butter in a very large (12-inch) cast iron skillet or any large oven-proof skillet, and cook the onions over low heat for 5 minutes, until softened. Add the garlic and cook for another few minutes, making sure not to burn it. Add the zucchini and squash and stir, the skillet should be pretty full at this point but the veggies will cook down. If you used a spiralizer and your veggies seem to be in one big string, cut them down a few times. Add the salt, pepper, herbes de provence, and nutmeg. Cover and cook for 10 minutes, or until tender. Uncover, stir, and check for seasonings. Stir in the flour. Add the hot milk and cook over low heat for a few minutes, until it makes a sauce.

Combine the panko, bread crumbs, and Gruyere and sprinkle on top of the zucchini mixture. If desired, dot with 1 tablespoon of butter, cut into small bits. Transfer skillet to oven and bake for 20 minutes, or until bubbly and browned.

*Note: If you do not have an oven proof skillet, feel free to transfer the veggie mixture into an 8×10 inch baking dish. We like the easy and rustic look of a cast iron skillet!