Zucchini Casserole Recipe

Creamy baked zucchini casserole in a white casserole dish and filled with rows of sliced zucchini and yellow squash and topped with a golden crust of panko breadcrumbs, and shredded cheese.

4.86 from 267 votes

This delicious Zucchini Casserole is a cheesy, creamy, and comforting side dish made with fresh zucchini and yellow squash, mayonnaise, sour cream, panko breadcrumbs, and lots of cheese.

Prep Time45

Cook Time40

Total Time1 25

Course: Casserole, Side Dish, Vegetables

Cuisine: American

Keyword: squash and zucchini casserole, zucchini casserole, zucchini casserole recipe

Servings: servings

Author: Jessica Randhawa

Ingredients

4 medium zucchini squash (sliced in 1/4" thick slices) see notes
salt
4 tablespoon butter divided
1 yellow onion finely chopped
2 cloves garlic minced
¼ black pepper
½ cup sour cream
½ cup mayonnaise
2 eggs slightly beaten
½ cup grated parmesan cheese
1 cup shredded cheddar cheese divided
½ cup shredded mozzarella cheese
1 cup panko breadcrumbs

US Customary - Metric

Instructions

Preheat the oven to 375 degrees Fahrenheit. Spray a 1.5 quart (1.5L) casserole dish with non-stick cooking spray.
Place the sliced zucchini in a large colander set over the kitchen sink. Toss the zucchini with salt (approximately 1-2 teaspoons). Drain the zucchini for at least 30-45 minutes. This step prevents us from ending up with a watery, soggy casserole. After the zucchini has drained, transfer them to a clean kitchen towel lined with paper towels. Gently pat the zucchini dry. Set aside.
As the zucchini slices drain, soften the onions. Add two tablespoons of butter to a medium skillet set over medium heat. Add the onions and cook, often stirring to prevent burning, until the onions have softened. At the last minute, add the minced garlic and black pepper. Mix well to combine, then remove from heat. Set aside to cool completely.
In a large bowl combine the sour cream, mayonnaise, eggs, grated parmesan cheese, ½ cup of shredded cheddar cheese, and ½ cup of mozzarella cheese. Once the onion and garlic mixture has cooled to room temperature, combine with the cheese mixture.
Transfer the drained zucchini slices to the prepared baking dish. Arrange in several overlapping rows. Additional salt is not needed.
Pour the creamy onion and cheese mixture directly over the top of the zucchini slices. Use a wooden spoon or spatula to smooth the surface.
Transfer to the oven and bake for 20 minutes.
Melt the remaining two tablespoons of butter in a small bowl in the microwave and combine with the panko breadcrumbs.
Carefully remove the casserole from the oven. Top with the panko breadcrumbs and the remaining half cup of shredded cheddar cheese. Return to the oven to bake for an additional 20-25 minutes, or until the cheese is melted and bubbly and the breadcrumbs are golden brown.

Notes

It is really hard to give an exact number of zucchini (or zucchini plus yellow squash) that you'll need to make this casserole. At a minimum, you'll need 4 medium-sized zucchini. I always make sure to have one extra squash on hand just in case.
Leftovers: Keep leftovers stored in an airtight container in the refrigerator for up to 4 days. Reheat in the oven preheated to 350 degrees F or in the microwave until heated through.
I do not recommend freezing.
To make this recipe gluten-free, you may either omit the breadcrumbs or purchase breadcrumbs that are certified gluten-free.

Nutrition