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A baked squash zucchini casserole with golden-brown topping

Classic Squash Zucchini Casserole

This classic squash zucchini casserole features tender sliced yellow squash and zucchini baked in a creamy, cheesy sauce. It's a comforting and flavorful side dish perfect for any meal.
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Prep Time 15 minutes
Cook Time 30 minutes
Total Time 45 minutes
Servings 6 people
Calories 350 kcal

Equipment

  • Oven
  • Large skillet
  • 9x13 inch baking dish
  • Whisk

Ingredients
  

Main Ingredients

  • 3 medium Yellow Squash sliced into 1/4-inch rounds
  • 3 medium Zucchini sliced into 1/4-inch rounds
  • 1 small Onion finely chopped
  • 2-3 cloves Garlic minced
  • 2 tablespoons Butter
  • 2 tablespoons All-Purpose Flour
  • 1.5 cups Milk full-fat or 2%
  • 0.5 cup Chicken or Vegetable Broth
  • 1.5 cups Cheddar Cheese shredded (divided)
  • 0.5 cup Parmesan Cheese freshly grated
  • 0.5 cup Sour Cream or Greek Yogurt
  • 2 tablespoons Fresh Parsley chopped
  • Salt To taste
  • Black Pepper To taste

Optional Topping

  • 0.5 cup Panko breadcrumbs
  • 1 tablespoon melted butter

Instructions
 

Preparation

  • Preheat the oven to 375°F (190°C) and lightly grease a 9x13 inch baking dish.
  • In a large skillet, melt 1 tablespoon of butter over medium heat, then sauté the sliced squash and zucchini for 5-7 minutes until slightly tender and some moisture has cooked out, then set them aside.

Make the Sauce

  • In the same skillet, melt the remaining 1 tablespoon of butter, add chopped onion and sauté for 3-5 minutes until softened, then stir in minced garlic and cook for another minute until fragrant.
  • Sprinkle flour over the onion and garlic, stirring constantly for 1 minute.
  • Gradually whisk in milk and broth, stirring until the mixture thickens and becomes smooth.
  • Remove the skillet from heat, stir in 1 cup of shredded cheddar cheese, all of the Parmesan cheese, and sour cream until well combined and melted, then season generously with salt and black pepper.

Assemble and Bake

  • Gently fold the sautéed squash and zucchini into the cheese sauce, then pour the mixture into the prepared baking dish, spreading evenly.
  • Sprinkle the remaining 1/2 cup of shredded cheddar cheese over the top, and if using, mix Panko breadcrumbs with melted butter and sprinkle over the cheese.
  • Bake for 25-30 minutes, or until bubbly and golden brown.
  • Allow the casserole to rest for 5-10 minutes before serving, then garnish with fresh chopped parsley.

Notes

For extra flavor, you can add a pinch of nutmeg to the cheese sauce. This casserole can be made ahead of time and reheated. Cover with foil before reheating in the oven until warmed through. If the top starts to brown too quickly, you can loosely cover it with foil during baking.