Summer Squash Casserole
This bright and comforting summer squash casserole is the perfect way to enjoy the season's bounty. A quick pre-salting step ensures the squash stays tender, not soggy, while a creamy, savory cheese sauce and a crispy, golden breadcrumb topping make every bite irresistible. It's an easy, crowd-pleasing dish for weeknight dinners or potlucks.
Equipment
- Large colander
- Mixing bowl
- Clean kitchen towel or paper towels
- Large skillet
- Whisk
- 8x8-inch baking dish (or 1.5-quart)
- Small bowl
- Knife
- Cutting board
- Measuring cups and spoons
Ingredients
- 2 medium yellow summer squash, sliced into ¼-inch rounds
- 2 medium zucchini, sliced into ¼-inch rounds
- 1 teaspoon salt for drawing out moisture
- 2 tablespoons unsalted butter
- 1 medium yellow onion, finely diced
- 2 cloves garlic, minced
- 2 tablespoons all-purpose flour
- 1 cup whole milk
- ½ cup sour cream
- 1 cup shredded sharp cheddar cheese, divided
- ½ cup grated Parmesan cheese, divided
- ½ cup panko breadcrumbs
- 2 tablespoons melted butter for the topping
- ¼ teaspoon black pepper
- ¼ teaspoon dried thyme optional
Instructions
- Place the sliced yellow squash and zucchini in a large colander set over a bowl. Toss with 1 teaspoon of salt and let sit for 15 minutes. Gently pat the slices dry with a clean kitchen towel or paper towels.
- In a large skillet over medium heat, melt 2 tablespoons of butter. Add the diced onion and cook, stirring occasionally, until softened and translucent, about 5 minutes. Add the minced garlic and cook for 30 seconds until fragrant.
- Sprinkle the flour over the onions and cook, stirring constantly, for 1 minute. Slowly pour in the milk while whisking continuously to prevent lumps. Bring to a gentle simmer and cook until thickened, about 2 minutes.
- Remove the skillet from the heat. Stir in the sour cream, ¾ cup of the shredded cheddar, and ¼ cup of the Parmesan cheese. Season with black pepper and dried thyme (if using).
- Preheat the oven to 375°F (190°C). Lightly grease an 8x8-inch baking dish.
- Gently fold the dried squash slices into the cheese sauce until evenly coated. Pour the mixture into the prepared dish and spread into an even layer.
- In a small bowl, combine the panko breadcrumbs with the remaining ¼ cup of cheddar, the remaining ¼ cup of Parmesan, and 2 tablespoons of melted butter. Stir until the crumbs are evenly moistened.
- Sprinkle the breadcrumb topping evenly over the casserole. Bake for 25-30 minutes, until the sauce is bubbly and the topping is deeply golden and crisp.
- Let the casserole rest for 5-10 minutes before serving to allow it to set.
Notes
Do not skip the salting step; it is crucial for preventing a watery casserole. For best results, grate your own cheese from a block, as pre-shredded cheese contains anti-caking agents that can affect the sauce's creaminess. This casserole can be assembled a day ahead and refrigerated; add 10 minutes to the baking time if baking from cold. Leftovers can be stored in an airtight container in the refrigerator for up to 3 days. Reheat in a 350°F oven until warmed through.