Zucchini Casserole Recipe (Easy, Cheesy & Customizable)
Zucchini has a habit of showing up in larger quantities than any one recipe can use, whether it comes from a garden that overproduced or a grocery bag that seemed like a good idea at the time. This zucchini casserole uses up several at once, with a creamy egg-and-sour-cream base under melted cheese and a buttery, crisp breadcrumb topping. Cooking and draining the zucchini first keeps the finished casserole sliceable instead of soupy.
Prep time: 15 minutes | Cook time: 45 minutes (about 10 in the skillet, 35 in the oven) | Cooling and resting: about 15 minutes | Total time: about 1 hour 15 minutes | Servings: about 8 as a side | Yield: one 9×13-inch casserole
Zucchini Casserole Ingredients
- 4 medium zucchini, sliced into rounds about 1/4 inch thick
- 1 small onion, diced
- 2 tbsp butter or olive oil, for the skillet
- 2 large eggs
- 1 cup sour cream (or homemade plain yogurt)
- 1 1/2 cups shredded cheddar cheese, divided
- 1/2 cup grated parmesan
- 1 cup breadcrumbs (panko gives the crispest top)
- 2 tbsp butter or olive oil, melted, for the topping
- 1 tsp garlic powder
- 1/2 tsp salt
- 1/4 tsp black pepper
- 2 tbsp chopped fresh herbs (parsley, thyme, or basil), optional
How to Make Zucchini Casserole
- Preheat. Heat the oven to 375°F (190°C) and lightly grease a 9×13-inch baking dish.
- Cook the zucchini. Melt the 2 tbsp of butter in a large skillet over medium heat and cook the onion until soft, 3 to 4 minutes. Add the zucchini and cook 5 to 6 minutes more, until just tender. Zucchini is mostly water, so it needs to give some up before it goes in the oven.
- Drain and cool. Move the zucchini and onion to a colander set over a bowl. Press gently with the back of a spoon and let it sit about 10 minutes. This drains the liquid and also cools the zucchini so it won’t start scrambling the eggs in the next step.
- Mix the base. In a large bowl, whisk the eggs and sour cream together. Stir in 1 cup of the cheddar, the parmesan, garlic powder, salt, and pepper.
- Combine. Fold the drained, cooled zucchini and onion into the egg mixture. Pour into the prepared dish and spread evenly.
- Add the topping. Sprinkle the remaining 1/2 cup cheddar over the top. Toss the breadcrumbs with the melted butter and scatter them over the cheese. Keeping the buttered crumbs on top, rather than under the cheese, lets them brown and crisp instead of steaming.
- Bake. Bake 30 to 35 minutes, until the top is golden and the center is set. The base contains eggs, so the center should read at least 160°F (71°C) on an instant-read thermometer. Rest 5 to 10 minutes before slicing so it firms up.
- Garnish and serve. Sprinkle with chopped fresh herbs, such as basil or thyme from a windowsill herb garden, if using. Serve warm.
Why Pre-Cooking the Zucchini Matters
Zucchini releases its water as soon as it heats. Put it into the egg mixture raw and that liquid has nowhere to go but into the custard, which turns loose and collects at the bottom of the dish. A short sauté and drain removes most of it beforehand. For very large or watery zucchini, you can also salt the slices and leave them in a colander for 15 to 20 minutes, then pat them dry and cut the added salt to 1/4 teaspoon. For most medium zucchini, the sauté-and-drain method above is enough.
Zucchini Casserole Variations
This casserole adjusts easily to whatever you have on hand:
- Add protein: Stir in cooked, crumbled bacon, diced ham, or about 2 cups of shredded cooked chicken for a chicken zucchini casserole that works as a main dish.
- Swap the cheese: Mozzarella, gruyère, or a Mexican cheese blend all work in place of cheddar.
- Make it lower-carb: Replace the breadcrumbs with crushed pork rinds, or skip the crumbs and add a little extra cheese.
- Add more vegetables: Diced bell pepper, corn, or halved cherry tomatoes fit well. Drain or pat dry anything moisture-heavy first so it doesn’t add water back in.
Storing and Reheating Zucchini Casserole
Refrigerate leftovers within 2 hours of baking. Leftover zucchini casserole keeps 3 to 4 days in a covered container. Reheat single portions in the microwave, or cover the dish with foil and warm it in a 350°F oven for about 15 minutes, uncovering for the last few minutes to bring some crunch back to the topping. Either way, heat it until steaming hot throughout (165°F/74°C on a thermometer).
It also freezes after baking, though the zucchini softens after thawing because of its water content. Cool it completely, wrap tightly or use an airtight container, and thaw overnight in the refrigerator before reheating.
Frequently Asked Questions
Why is my zucchini casserole watery?
It’s usually one of three things: zucchini that wasn’t drained well (see the section above), moisture-heavy add-ins like tomatoes that weren’t patted dry, or a center that hadn’t fully set before slicing. If the middle still jiggles at 30 minutes, give it another 5 to 10 and check that it reaches 160°F.
Can I make zucchini casserole ahead of time?
Assemble it through the cheese layer, cover, and refrigerate, making sure the cooked zucchini has cooled before it goes into the egg mixture. Bake within 24 hours, since the base contains raw eggs, and add a few extra minutes if it goes into the oven cold. Check the center for doneness rather than relying on time alone. For the crispiest topping, toss the buttered crumbs on just before baking.
Can I use shredded zucchini instead of sliced?
You can, but shredded zucchini holds even more water than rounds. Squeeze it in a clean kitchen towel or cheesecloth until it stops dripping before it goes into the base.
Do I need to peel the zucchini?
No. The skin is thin and tender, and it adds color and a little texture.
Can I use yellow squash instead of zucchini?
Yes, in equal amounts. Yellow squash swaps in directly, and a mix of the two makes a good zucchini and squash casserole.
