This Zucchini Casserole is a creamy, cheesy, and comforting side dish made with fresh zucchini (and optional yellow squash), sour cream, mayonnaise, panko breadcrumbs, and plenty of cheese. Simple to prepare and crowd-pleasing, it pairs well with chicken, beef, fish, or holiday mains.
This irresistible zucchini casserole is rich, creamy, and full of melty cheese. Mild zucchini absorbs the flavors around it, making this dish a great way to add vegetables to the plate without sacrificing flavor.
Key Ingredients and Substitutions
Printable measurements appear in the recipe card below.
- Zucchini: Use at least four medium zucchini (or a mix of zucchini and yellow squash). Have one extra on hand if squash sizes vary.
- Butter: Used for sautéing the onion and garlic; olive oil can be substituted.
- Garlic: Freshly minced for the best flavor.
- Onion: Finely chopped yellow onion, sautéed until soft.
- Sour cream: Adds creaminess and a pleasant tang; full-fat preferred.
- Mayonnaise: Combined with sour cream and cheese for a rich sauce.
- Eggs: Lightly beaten, they help thicken the filling.
- Cheese: A mix of grated Parmesan, shredded cheddar, and shredded mozzarella gives flavor and stretch.
- Panko breadcrumbs: Provide a crisp, buttery topping. Omit or replace for gluten-free or low-carb versions.
Is it Keto?
The casserole as written contains breadcrumbs, so it’s not fully keto. To make it keto-friendly, skip the panko or swap in a low-carb alternative such as crushed pork rinds or a keto breadcrumb substitute.
How to Make It
1. Preheat the oven to 375°F. Spray a 1.5-quart casserole dish with non-stick spray.
2. Prepare the zucchini: Slice zucchini into 1/4-inch rounds. Toss with 1–2 teaspoons of salt and place in a colander over the sink to drain for 30–45 minutes. After draining, transfer to a clean towel and gently pat dry to remove excess moisture.
3. Sauté the aromatics: Melt 2 tablespoons butter in a skillet over medium heat. Add finely chopped onion and cook until softened. Stir in minced garlic and black pepper at the end, then remove from heat and let cool.
4. Make the creamy cheese mixture: In a large bowl, combine sour cream, mayonnaise, eggs, grated Parmesan, 1/2 cup shredded cheddar, and 1/2 cup shredded mozzarella. Fold in the cooled onion and garlic. Additional salt is usually unnecessary because the mixture and cheese add plenty of seasoning.
5. Assemble: Arrange the dried zucchini slices in overlapping rows in the prepared dish. Pour the creamy mixture evenly over the zucchini and smooth the top.
6. Bake for 20 minutes. While the casserole bakes, melt the remaining 2 tablespoons butter and mix with the panko breadcrumbs.
7. Remove the casserole, sprinkle with the panko-butter mixture and the remaining 1/2 cup shredded cheddar, then return to the oven and bake another 20–25 minutes until the top is golden and the filling is bubbly.
Tools for this Recipe
Helpful items for this recipe include a 1.5-quart baking dish, a colander for draining the zucchini, a skillet for sautéing, a box grater for shredding cheese, and mixing bowls.
What to Serve with It
This casserole makes a flavorful side for baked salmon, pan-seared steak, roasted chicken, or a holiday spread. It’s rich enough for special occasions yet easy enough for weeknight dinners.
Storage and Freezing
Store leftovers in an airtight container in the refrigerator for 3–4 days. Reheat in the oven at 350°F or in the microwave until warmed through. Freezing is not recommended because the texture changes after thawing.
More Zucchini Recipes
- Roasted Zucchini with Parmesan
- Zucchini Boats
- How to Make and Cook Zucchini Noodles (Zoodles)
- Baked Zucchini Fries
- Sautéed Zucchini
- Cheesy Zucchini Bread (Quick Bread)
- Healthy Corn and Zucchini Chowder
Zucchini Casserole Recipe
Ingredients
- 4 medium zucchini, sliced into 1/4″ rounds
- Salt, for draining the zucchini
- 4 tablespoons butter, divided
- 1 yellow onion, finely chopped
- 2 cloves garlic, minced
- Pinch of black pepper
- 1/2 cup sour cream
- 1/2 cup mayonnaise
- 2 eggs, slightly beaten
- 1/2 cup grated Parmesan
- 1 cup shredded cheddar, divided
- 1/2 cup shredded mozzarella
- 1 cup panko breadcrumbs
Instructions
- Preheat oven to 375°F and grease a 1.5-quart casserole dish.
- Toss zucchini slices with 1–2 teaspoons salt and drain in a colander for 30–45 minutes. Pat dry on a towel to remove excess moisture.
- Sauté chopped onion in 2 tablespoons butter until soft. Add garlic and pepper at the end, then remove from heat and cool.
- In a large bowl, mix sour cream, mayonnaise, eggs, Parmesan, 1/2 cup cheddar, and 1/2 cup mozzarella. Stir in cooled onions and garlic.
- Arrange zucchini in overlapping rows in the prepared dish. Pour the creamy mixture over the zucchini and smooth the top.
- Bake 20 minutes. Meanwhile, melt remaining 2 tablespoons butter and toss with panko breadcrumbs.
- Remove casserole, top with the panko mixture and remaining cheddar, then bake 20–25 more minutes until bubbly and golden.
Notes
- Quantity of zucchini can vary; plan for at least four medium squash and keep an extra on hand if needed.
- Leftovers keep 3–4 days refrigerated. Reheat in the oven at 350°F or in the microwave.
- Freezing is not recommended due to texture changes.
- To make gluten-free, omit the panko or use certified gluten-free breadcrumbs.
Nutrition (per serving)
Nutrition values are estimates and should be used as a guide.