Zucchini Casserole turns a pile of summer zucchini into a cheesy, golden side dish: grated zucchini and onion, salted and squeezed dry, mixed with eggs, Greek yogurt, Parmesan and a little Dijon, then topped with sharp cheddar and buttery panko and baked until the edges bubble. It serves 10 and bakes in a 9×13-inch dish.
How to make it: Grate the zucchini, salt it with the onion, let it sit 20 minutes and squeeze out the liquid. Stir it into the egg, yogurt, Parmesan and panko mixture, spread it in the dish, top with cheddar and buttered panko, and bake at 375°F for 35 to 45 minutes, until deep golden.
Why You’ll Love It
- Uses a lot of zucchini: 2 1/2 pounds, about 6 to 8 medium, go into one dish.
- Not watery: salting and squeezing the zucchini takes care of the extra moisture.
- Crispy top, creamy middle: buttered panko over a cheesy filling.
- A side for a crowd: 10 servings from one 9×13-inch pan.
Ingredient Notes
Zucchini: Two and a half pounds, grated on the large holes of a box grater. No need to peel it.
Onion: One small yellow onion, finely chopped or grated, about a cup. It gets salted and squeezed along with the zucchini.
Kosher salt: Two teaspoons draw the water out of the zucchini; the last half teaspoon seasons the filling.
Eggs and Greek yogurt: Three large eggs and 2/3 cup of full-fat plain Greek yogurt hold everything together. Sour cream works in place of the yogurt.
Cheese: Two and a half ounces of finely grated Parmesan in the filling and 4 ounces of shredded sharp cheddar on top.
Panko: One and a quarter cups in the filling for body, and half a cup tossed with melted butter for the crunchy top.
Seasonings: Dijon mustard, garlic powder, dried oregano and black pepper.
Ingredients
- Cooking spray
- 2 1/2 pounds zucchini (6 to 8 medium)
- 1 small yellow onion, finely chopped or grated (about 1 cup)
- 2 1/2 teaspoons kosher salt, divided
- 1 3/4 cups panko breadcrumbs, divided
- 2 1/2 ounces Parmesan cheese, finely grated (about 2/3 cup)
- 3 large eggs
- 2/3 cup full-fat plain Greek yogurt or sour cream
- 2 teaspoons Dijon mustard
- 1 teaspoon garlic powder
- 1/2 teaspoon dried oregano
- 1/4 teaspoon freshly ground black pepper
- 4 ounces sharp cheddar cheese, shredded (about 1 1/4 cups)
- 2 tablespoons unsalted butter, melted, or olive oil
How to Make Zucchini Casserole
1. Heat the oven. Heat the oven to 375°F. Coat a 9×13-inch baking dish with cooking spray.
2. Salt and squeeze the zucchini. Grate the zucchini on the large holes of a box grater. Put it in a colander in the sink with the onion, sprinkle with 2 teaspoons of the salt and stir. Let it sit 20 minutes, then squeeze out the extra liquid by the handful; it doesn’t need to be perfectly dry.
3. Mix the filling. In a large bowl, stir together 1 1/4 cups of the panko, the Parmesan, eggs, yogurt, Dijon, garlic powder, oregano, the remaining 1/2 teaspoon salt and the pepper. Stir in the zucchini and onion.
4. Top. Spread the mixture in the dish and sprinkle with the cheddar. In the same bowl, stir the remaining 1/2 cup panko with the melted butter and scatter it over the top.
5. Bake. Bake 35 to 45 minutes, until the edges bubble, the breadcrumbs are deep golden brown and the center reaches 160°F.
How to Keep Zucchini Casserole From Getting Watery
Zucchini is mostly water. Left alone, it releases that water in the oven and leaves a soggy casserole sitting in a puddle. The fix happens before anything goes in the dish.
Salt it and wait. Salt pulls moisture out of the zucchini. Grated zucchini and onion need 20 minutes in a colander with 2 teaspoons of kosher salt.
Squeeze, don’t just drain. Grab the grated zucchini by the handful and squeeze hard over the sink, or twist it in a clean kitchen towel. It doesn’t have to be bone dry; just get most of the liquid out.
Sliced instead of grated? Cut the slices thick, about 1/2 inch, salt them in a towel-lined colander and let them sit at least 15 minutes, better 30 to 45, then blot them dry.
Don’t over-bake. Past the point of tender, zucchini goes mushy. Take it out once the edges bubble and the top is deep golden.
| Zucchini cut | Salt and rest | Then |
|---|---|---|
| Grated (this recipe) | 20 minutes in a colander | Squeeze out by the handful |
| Thick slices | 15 minutes, better 30 to 45 | Blot dry with towels |
Tips for Success
Do I need to peel the zucchini?
No. Grate it skin and all; the peel adds color to the casserole.
Can I use sour cream instead of Greek yogurt?
Yes. Use the same 2/3 cup of full-fat sour cream.
Variations
- Layered mozzarella: layer 4 medium zucchini, cut into 1/2-inch rounds, three times with 8 ounces of mozzarella, 1/3 cup of Parmesan, parsley and salt in an oiled 8×8-inch dish. Top with 1/2 cup seasoned breadcrumbs stirred into 2 tablespoons of melted butter and bake at 375°F for 45 to 50 minutes.
- Creamy with a cracker top: mix grated, squeezed zucchini with 1/2 cup each of sour cream and mayonnaise, garlic and onion powder, 3 eggs, cheddar and Parmesan. Bake 30 minutes, then top with crushed butter crackers and more cheddar and bake 10 to 15 minutes more. Let it rest 10 minutes before slicing.
- Three cheeses: cover salted, blotted zucchini slices with a mix of eggs, cheddar, mozzarella, Parmesan and Italian seasoning, bake 20 minutes, then add buttered panko and more cheddar and bake about 20 minutes more.
- Feta and herbs: use sliced zucchini with feta, heavy cream, an egg, basil, thyme and oregano under panko, covered for 25 minutes, then Parmesan on top for 5 more.
- With yellow squash: sauté zucchini, yellow summer squash, onion and carrots, stir in cream of mushroom soup, yogurt and herb-seasoned stuffing mix, top with more buttered stuffing and bake at 350°F for about 30 minutes.
Storage & Reheating
USDA FSIS says to refrigerate leftovers within 2 hours in shallow, covered containers and eat them within 3 to 4 days, or freeze them for 3 to 4 months. Thaw frozen casserole in the refrigerator, never on the counter. Reheat it in the oven, so the top crisps up again, until it reaches 165°F.
What to Serve With It
It’s a side dish for grilled chicken, pork chops or a summer cookout. For more zucchini, try skillet zucchini and mushrooms, baked zucchini fries, roasted garlic-Parmesan zucchini, squash and tomatoes or garlic herb roasted potatoes, carrots and zucchini. Other summer sides: patty pan squash and easy creamy corn casserole.
Frequently Asked Questions
What are the tips for the best zucchini casserole?
Salt the zucchini and squeeze out the liquid before mixing, use eggs and a thick dairy like Greek yogurt to bind it, top it with buttered panko, and don’t over-bake it.
Why is my zucchini casserole watery?
The zucchini wasn’t salted and squeezed first. Give grated zucchini 20 minutes in a colander with salt, then squeeze out as much liquid as you can.
Can I use sliced zucchini?
Yes. Slice it about 1/2 inch thick, salt and drain the slices at least 15 minutes, blot them dry, and try the layered or three-cheese version.
How do I know it’s done?
The edges bubble, the breadcrumbs are deep golden brown, and the center reaches 160°F.
Can I freeze zucchini casserole?
Yes, for 3 to 4 months. Thaw it in the refrigerator and reheat it in the oven to 165°F.
Final Notes
Don’t skip the squeeze; it’s the difference between a sliceable casserole and a soupy one. If you make it, tell me in the comments what you served it with.
Zucchini Casserole
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Ingredients
- cooking spray
- 2 1/2 pounds zucchini 6 to 8 medium
- 1 small yellow onion finely chopped or grated, about 1 cup
- 2 1/2 teaspoons kosher salt divided
- 1 3/4 cups panko breadcrumbs divided
- 2 1/2 ounces Parmesan cheese finely grated, about 2/3 cup
- 3 large eggs
- 2/3 cup plain Greek yogurt full-fat, or sour cream
- 2 teaspoons Dijon mustard
- 1 teaspoon garlic powder
- 1/2 teaspoon dried oregano
- 1/4 teaspoon black pepper freshly ground
- 4 ounces sharp cheddar cheese shredded, about 1 1/4 cups
- 2 tablespoons unsalted butter melted, or olive oil
Instructions
- Heat the oven to 375°F. Coat a 9x13-inch baking dish with cooking spray.
- Grate the zucchini on the large holes of a box grater. Put it in a colander in the sink with the onion, sprinkle with 2 teaspoons of the salt and stir. Let it sit 20 minutes, then squeeze out the extra liquid by the handful; it doesn't need to be perfectly dry.
- In a large bowl, stir together 1 1/4 cups of the panko, the Parmesan, eggs, yogurt, Dijon, garlic powder, oregano, the remaining 1/2 teaspoon salt and the pepper. Stir in the zucchini and onion.
- Spread the mixture in the dish and sprinkle with the cheddar. In the same bowl, stir the remaining 1/2 cup panko with the melted butter and scatter it over the top.
- Bake 35 to 45 minutes, until the edges bubble, the breadcrumbs are deep golden brown and the center reaches 160°F.
