Summer Squash Casserole

This summer squash casserole is a southern classic made with seasonal fresh zucchini and yellow squash! The cheesy filing is topped with crispy french fried onions for the perfect side dish!

Course Side Dish

Cuisine American, Southern

Diet Vegetarian

Prep Time 20

Cook Time 45

Total Time 1 5

Servings

Calories 268kcal

Author Kyleigh Sage

Equipment

Ingredients

2 medium zucchini thinly sliced
2 medium yellow squash thinly sliced
3 tablespoons unsalted butter divided
1 small yellow onion diced
2 cloves garlic finely chopped
1 ½ teaspoons kosher salt divided
½ cup plain full-fat Greek yogurt substitute sour cream
½ cup whole milk
2 large eggs beaten
1 ½ cups shredded cheddar cheese divided
2 teaspoons fresh thyme optional
1 teaspoon lemon juice
½ teaspoon black pepper
¼ teaspoon cayenne pepper optional
1 cup french fried onions

US Customary - Metric

Instructions

Thinly slice the zucchini and squash to about ¼ inch thick (I like using a mandoline to slice the squash quickly). You need about 2 pounds of total squash, which is equivalent to about 2 medium zucchini and 2 medium yellow squash. After the squash is all sliced, you should have about 6 cups total.
Preheat the oven to 375°F.
In a large skillet over medium high heat, saute the onion and garlic in 1 tablespoon of butter for about 5 minutes or until softened. Then transfer to a large mixing bowl.
In the same skillet, melt the remaining 2 tablespoons of butter and then add in the sliced squash and ½ teaspoon of salt. Cook over medium heat, stirring frequently, for about 10 minutes or until the squash has softened.
Transfer to a colander and let all the excess liquid drain away for at least 5 minutes.
In the large mixing bowl with the cooked onions, add in the Greek yogurt, milk, eggs, 1 cup of shredded cheese, thyme, lemon juice, remaining salt, pepper, and cayenne and gently mix until fully combined.
Then add in the cooked and drained squash and stir gently to combine, making sure every piece of squash is coated in the sauce.
Transfer to a baking dish and sprinkle with the remaining shredded cheese, then bake uncovered at 375°F for 35 minutes.
If desired, top with french fried onions and bake for another 10 minutes.
Remove from the oven and serve warm!

Notes

To prep this casserole in advance: Prep everything and place it in the casserole dish, then cover and refrigerate for up to 2 days. When you're ready to bake, remove from the fridge and let sit at room temperature for at least 30 minutes before baking (this ensures the casserole will get fully cooked in the middle and also protects your casserole dish from cracking due to temperature change). Then bake and top with french fried onions as normal!

Optional Cracker Topping (instead of french fried onions)

1 sleeve Ritz crackers
2 tablespoons unsalted butter, melted

Gently crush the Ritz crackers until you have small chunks.
In a small bowl, combine the crushed crackers and melted butter.
Make the casserole as directed and bake for 20 minutes. Then sprinkle the cracker mixture on top and bake for another 20-30 minutes or until golden brown and bubbling.

Nutrition