Best Zucchini Casserole Recipe

This creamy zucchini casserole transforms humble summer squash into an absolutely irresistible side dish that rivals any holiday favorite with its rich, cheesy sauce and golden crispy topping. Thinly sliced zucchini gets nestled in a luxurious cream sauce infused with sharp cheddar, Parmesan, and fresh thyme, then crowned with buttery panko breadcrumbs that bake to perfect golden perfection. The result is a sophisticated comfort food that proves zucchini deserves a starring role on your dinner table, not just a supporting one, while using up those abundant summer garden harvests in the most delicious way possible.

I developed this recipe during a particularly abundant zucchini summer when my garden was producing faster than my family could possibly eat fresh squash. After trying countless zucchini bread and muffin recipes, I wanted something savory and substantial that would showcase the vegetable rather than hide it. This casserole was an instant hit with my family, including my teenage son who claimed he didn't like zucchini but went back for seconds. Now it's become our go-to way to use up summer squash while creating something that feels special enough for company.

Ingredients

• Medium zucchini (2 lbs, about 4-5 zucchini): Choose firm, unblemished squash and slice them uniformly thin for even cooking
• Kosher salt (2 teaspoons): Essential for drawing out excess moisture that would otherwise make the casserole watery
• Yellow onion (1 medium, diced): Provides aromatic foundation and natural sweetness that complements the zucchini beautifully
• Unsalted butter (4 tablespoons, divided): Used for sautéing and creating the rich, golden topping
• All-purpose flour (3 tablespoons): Thickens the sauce to perfect creamy consistency
• Chicken or vegetable broth (1 cup): Adds depth of flavor while providing liquid for the sauce base
• Whole milk (3/4 cup): Creates smooth, creamy texture without excessive richness
• Plain Greek yogurt (1/2 cup, whole milk variety): Adds tanginess and richness that won't curdle during baking
• Sharp cheddar cheese (1 cup, shredded): Provides bold, melty cheese flavor that defines this casserole
• Parmesan cheese (1/2 cup, grated, divided): Adds nutty, salty complexity to both sauce and topping
• Fresh thyme (2 teaspoons, chopped): Bright herbal notes that elevate the entire dish
• Garlic powder (1 teaspoon): Subtle garlic flavor that enhances without overpowering
• Black pepper (1/2 teaspoon): Adds gentle warmth and complexity
• Panko breadcrumbs (1 cup): Creates that essential crispy contrast to the creamy interior
• Extra Parmesan cheese (1/4 cup, grated): Adds extra cheesy goodness to the golden topping

Instructions

Prepare the zucchini to remove excess moisture:

Slice the zucchini into thin rounds, about 1/8 inch thick for even cooking. Place in a large colander, toss with kosher salt, and let drain for 30 minutes. This crucial step prevents a watery casserole.

Preheat oven and prepare your baking dish:

Set oven to 400°F and lightly grease a 9x13 inch baking dish. Having everything ready before you start cooking makes the process much smoother.

Sauté the onions until softened and fragrant:

In a large Dutch oven or heavy-bottomed skillet, melt 2 tablespoons butter over medium heat. Add diced onions and cook for 5-6 minutes until softened and translucent but not browned.

Create the roux base for thickening:

Sprinkle flour over the cooked onions and stir constantly for 1-2 minutes to cook out the raw flour taste. This creates the foundation for a smooth, lump-free sauce.

Gradually add liquids to create smooth sauce:

Slowly pour in the broth while whisking constantly, followed by the milk. Continue cooking while stirring until the mixture thickens enough to coat the back of a spoon, about 3-4 minutes.

Thoroughly dry the salted zucchini:

Pat the drained zucchini completely dry with paper towels or clean kitchen towels. Any remaining moisture will make your casserole watery, so this step is essential.

Finish the creamy sauce off the heat:

Remove the pan from heat and whisk in the Greek yogurt until smooth. Add the cheddar cheese, stirring until melted, then mix in half the Parmesan, thyme, garlic powder, and pepper.

Gently fold in the prepared zucchini:

Add the dried zucchini to the sauce in batches, folding gently to coat each piece without breaking the delicate slices. Mix in half the panko breadcrumbs for extra body.

Transfer to baking dish and create topping:

Spread the zucchini mixture evenly in the prepared baking dish. Melt the remaining butter and mix with remaining panko and Parmesan, then sprinkle over the casserole.

Bake until golden and bubbly:

Bake for 30-35 minutes until the top is golden brown and the edges are bubbling. Let rest for 5-10 minutes before serving to allow the sauce to thicken slightly.

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The Critical Importance of Draining Zucchini

The single most important step in this recipe is properly removing moisture from the zucchini before baking. Zucchini has incredibly high water content, and if you skip the salting and draining process, you'll end up with a soupy, unappetizing mess instead of the creamy, cohesive casserole you want. The salt draws out excess water through osmosis, concentrating the zucchini's flavor while preventing it from releasing moisture during baking. After salting, thorough drying with paper towels removes both the salt and the extracted water, leaving you with zucchini that will maintain its texture and not dilute your carefully crafted sauce.

Building the Perfect Creamy Sauce

The sauce in this casserole strikes the perfect balance between richness and lightness by using a combination of milk, Greek yogurt, and cheese rather than relying solely on heavy cream. The Greek yogurt adds tangy complexity while providing creaminess without excessive calories, and it won't curdle during the baking process like some dairy products might. Creating a proper roux with the flour and onions ensures your sauce will be smooth and lump-free while providing enough body to coat the zucchini beautifully. The gradual addition of liquids while whisking constantly prevents lumps from forming and creates that silky texture that makes this casserole so appealing.

Achieving the Perfect Golden Topping

The panko and Parmesan topping is what transforms this from a simple creamed vegetable into something truly special. Panko breadcrumbs create much better texture than regular breadcrumbs because they're larger and stay crispier during baking. Mixing them with melted butter ensures even browning and prevents dry spots. The addition of Parmesan cheese to the topping provides extra flavor and helps create that beautiful golden color that makes this casserole so visually appealing. If you want an even crispier top, place the finished casserole under the broiler for the last minute or two of cooking.

Make-Ahead and Storage Strategies

This casserole is perfect for entertaining because it can be assembled completely up to 24 hours ahead of baking. Just cover tightly and refrigerate, then bring to room temperature for 30 minutes before baking. You might need to add 5-10 extra minutes to the baking time if starting from cold. Leftovers keep beautifully in the refrigerator for up to four days and reheat well in either the oven or microwave. The texture stays remarkably good, making this an excellent candidate for meal prep or planned leftovers that actually improve with time as the flavors continue to develop.

Creative Variations and Add-Ins

While this recipe is absolutely perfect as written, it welcomes many delicious variations based on your preferences or what you have available. Adding cooked ground meat like turkey, beef, or sausage transforms it into a complete one-dish meal that can serve as a main course rather than just a side. Different cheese combinations work beautifully too - try Gruyere for sophistication, or add some cream cheese for extra richness. Yellow summer squash can replace part of the zucchini for color variation, while fresh herbs like basil or oregano create different flavor profiles that complement various main dishes.

Serving Suggestions and Pairings

This rich, creamy casserole pairs beautifully with simple roasted or grilled meats that don't compete with its luxurious texture. Roasted chicken, grilled pork tenderloin, or baked salmon all complement the cheesy, herbed flavors while providing protein balance to the vegetable-based dish. For holiday meals, this casserole fits perfectly alongside traditional favorites like green bean casserole and stuffing, providing a sophisticated alternative that uses seasonal produce. The golden top and creamy interior make it visually appealing enough for special occasions while being approachable enough for everyday family dinners.

I love how this recipe has become my answer to abundant zucchini harvests while creating something that feels truly special rather than just a way to use up excess vegetables. Every time I serve this casserole, people are surprised by how sophisticated and delicious it is, proving that humble ingredients can become extraordinary when treated with care and creativity. It's become one of my most requested recipes for potlucks because it's substantial enough to satisfy hearty appetites while being refined enough for elegant gatherings.

This zucchini casserole represents everything I love about seasonal cooking - taking advantage of abundant summer produce and transforming it into something that celebrates the ingredient while creating comfort and satisfaction. Every time I make this dish, I'm reminded that the best recipes often come from necessity combined with creativity, turning what could be a challenge into an opportunity to create something truly delicious.

Frequently Asked Questions

→ Can I make this zucchini casserole ahead of time?

Yes, you can assemble the casserole up to 1 day ahead and refrigerate. Add 10-15 minutes to the baking time if cooking from cold.

→ How do I keep zucchini casserole from being watery?

Salt the sliced zucchini and let it drain for at least 20 minutes, then pat completely dry with paper towels before adding to the sauce.

→ Can I freeze leftover zucchini casserole?

Freezing is not recommended as the zucchini becomes mushy and watery when thawed. Store leftovers in the fridge for up to 4 days instead.

→ What can I substitute for Greek yogurt in this recipe?

You can use sour cream or heavy cream instead of Greek yogurt. Use the same amount and add it after removing the sauce from heat.

→ How do I know when the zucchini casserole is done?

The casserole is ready when it's bubbling around the edges, the top is golden brown, and the zucchini feels tender when pierced with a fork.

→ Can I use different types of cheese?

Yes, try Gruyere, Swiss, or mozzarella instead of cheddar. Just make sure to use good melting cheeses for the best texture.