Summer Squash Gratin

2 tablespoons butter
1/2 white onion, thinly sliced
1 medium zucchini, sliced 1/4-inch thick
1 medium yellow squash, sliced 1/4-inch thick
2 cloves garlic, minced
1 tablespoon fresh thyme leaves
1/2 cup heavy cream
1/4 cup Parmesan, grated
1 cup Gruyere or Swiss cheese, grated
Kosher salt and freshly ground black pepper, to taste

Preheat oven to 450°F.

In a 6 to 8-inch oven-safe skillet, heat butter over medium heat. Add onion and cook until soft, about 4 minutes. Add garlic and cook 1 minute more.

Stir in cream, thyme, and salt and pepper and let cook until starting to thicken.

Stir in parmesan and squash and let bubble for 2-3 minutes. Spread squash out evenly, top with Gruyere cheese and bake until bubbly and golden brown, about 20 minutes. Let rest 5 minutes before serving. Enjoy!