Zucchini, Squash & Corn Casserole — Creamy, Cheesy, & Summer‑Vibe Side Dish
There’s something wonderful about a bake that captures the best of summer vegetables — sweet corn, tender zucchinis, yellow squash — all enveloped in a creamy, cheesy mixture with a golden topping. This Zucchini, Squash & Corn Casserole is that kind of dish: comforting, satisfying, and great for potlucks, cookouts, or family dinners. It’s also nice make‑ahead, and you can freeze or prep it ahead of baking.
Why You’ll Love It
- Uses fresh summer produce (or frozen/canned if needed) for flavor and texture
- Creamy & cheesy base balanced by crunchy, buttery topping
- One baking dish, relatively simple prep, forgiving recipe
- Works great as side dish but hearty enough to enjoy on its own
- Forms beautiful layers; leftovers reheat well
Key Ingredients
Here are the main ingredients for about 8 servings (side dish). Adjust up/down depending on your pan size / how much you want.
| Ingredient | Quantity | Purpose / Notes |
|---|---|---|
| Yellow squash | ~1½ lb, thinly sliced | provides color, mild flavor |
| Zucchini | ~1½ lb, thinly sliced | classic summer squash contrast |
| Sweet yellow onion | 2 cups diced | flavor base |
| Garlic | 2 cloves minced | aroma & depth |
| Corn kernels | 3 cups | fresh or frozen works, sweet + texture |
| White cheddar cheese | 1½ cups shredded | creaminess + cheesy flavor |
| Sour cream | ½ cup | richness, slight tang |
| Mayonnaise | ½ cup | helps with creaminess + binder |
| Eggs | 2, lightly beaten | helps set the filling so it holds together |
| Butter | ¼ cup divided | part for sauté / part for topping |
| Salt & Pepper | ~1 tsp salt, ~2 tsp pepper (adjust to taste) | seasoning foundation |
| Fresh breadcrumbs | 1½ cups, divided | part inside; part for crispy topping |
| Parmesan (or Asiago) cheese | 1 cup, grated/soft, divided | gives sharp, nutty flavor and crust |
| Optional herbs / seasoning tweaks | e.g. garlic powder, thyme, paprika | personal flavor touch |
Based on Plain Chicken’s version: squash + zucchini, corn, cheese, sour cream + mayo + eggs, breadcrumbs + Parmesan topping.
Equipment & Prep
- 9×13‑inch baking dish
- Skillet for sautéing
- Mixing bowls
- Knife / cutting board
- Cheese grater
- Measuring cups & spoons
How To Make It — Step by Step
Here’s how to build this casserole to get creamy inside, golden, crunchy on top, with good texture.
Step 1: Preheat & Prepare Pan
- Preheat your oven to 350°F (≈ 175°C).
- Grease your 9×13‑inch baking dish (or equivalent) (spray or butter).
Step 2: Sauté Vegetables
- Melt half the butter (about 2 Tbsp) in a large skillet over medium heat.
- Add diced onion and sauté until softened and slightly translucent — about 5‑7 minutes.
- Add garlic; cook another ~1‑2 minutes until fragrant.
- Add the thinly sliced yellow squash and zucchini; cook, stirring occasionally, until tender but not mushy — about 8‑10 minutes. Squash and zucchini release water, so let some moisture cook off.
- Stir in the corn kernels near the end to warm through. Remove from heat.
Step 3: Combine the Creamy Filling
- In a large bowl, mix together sour cream, mayonnaise, eggs, shredded white cheddar cheese, salt, pepper, and any optional seasonings (garlic powder, thyme, paprika).
- Fold in the sautéed squash, zucchini, onion, and corn.
- Add half of the breadcrumbs (about ½ of what you reserved) plus half of the Parmesan (or Asiago) cheese into the mixture. Stir gently until evenly distributed.
Step 4: Assemble in the Baking Dish
- Transfer the mixture into the prepared baking dish, spreading it evenly.
Step 5: Make & Add the Topping
- Melt the remaining butter (~2 Tbsp).
- In a bowl, mix the remaining breadcrumbs + remaining Parmesan (or Asiago) cheese + melted butter.
- Sprinkle this evenly over the top of the casserole. This topping gives golden color and a satisfying crunch.
Step 6: Bake
- Bake uncovered in preheated oven for 45‑50 minutes, or until the top is golden brown and the edges are bubbling.
- If the top browns too rapidly before the filling is fully set, loosely cover with foil for part of the bake.
Step 7: Rest & Serve
- Once baked, let the casserole rest for 5‑10 minutes before serving. This helps the filling settle so slices hold together.
- Garnish with fresh herbs (parsley, chives, thyme) if you like.
- Serve warm. Goes well with grilled meats, roasted chicken, or even as a vegetarian main.
Tips for Best Results
- Use freshly shredded cheese rather than pre‑shredded, for better melt and texture.
- Slice squash and zucchini thinly but not paper‑thin—so they cook evenly and still hold texture.
- Drain excess liquid from veggies if needed; moist squash can make the casserole watery.
- Topping is key: buttered breadcrumbs + cheese gives the crispiness contrast.
- Make ahead: you can assemble the casserole (even freeze it) and bake when ready. Plain Chicken notes you can refrigerate overnight or freeze unbaked.
Variations & Substitutions
Here are ways to change or adapt the casserole to your taste, dietary needs, or what you have.
| Variation | What to Change / Add |
|---|---|
| Gluten‑Free | Use gluten‑free breadcrumbs or omit them; replace with crushed nuts or gluten‑free cracker crumbs. |
| Lighter / Lower Fat | Use low‑fat sour cream or Greek yogurt; reduce cheese or use leaner cheese; use olive oil instead of part of the butter. |
| Extra Veggies | Add bell pepper, mushrooms, or even diced tomatoes. Use pretty equal amounts. |
| Spicy Version | Add chopped jalapeño, red pepper flakes, or even a dash of hot sauce. |
| Different Cheeses | Swap cheddar for Pepper Jack, Mozzarella, Gruyère, or a mix for interesting flavor. |
| Herb‑Enhanced | Add chopped fresh herbs like thyme, oregano, basil either in filling or as garnish. |
| Make It Vegan | Use vegan cheese, vegan sour cream or yogurt, and skip butter / use plant‑based fat; use egg substitute if needed. |
Storage, Freezing & Reheating
- Make‑Ahead: You can fully assemble the casserole ahead of time, cover, refrigerate overnight. Bake when ready; might need a few extra minutes.
- Freezing: Good option. Plain Chicken says you can divide into pans, freeze one unbaked, then thaw fully before baking.
- Refrigeration: Leftovers keep well in airtight container for ~3‑4 days. Reheat in oven or microwave; adding a bit of milk or cream helps if it has dried out.
- Reheating Tip: Warm in oven at ~325°F until heated through; top can be crisped a bit under broiler if needed.
Frequently Asked Questions
Q: Can I use frozen corn instead of fresh?
Yes — thaw and drain well. Flavor will still be good.
Q: Do I need to peel the squash or zucchini?
Not necessary; the skins are edible and contain nutrients. If skin is thick or waxed, you can peel partially or use younger, thinner skinned ones.
Q: My casserole is watery — what went wrong?
Possible causes: squash/zucchini released too much water and wasn’t cooked off or drained; not enough binder (eggs/cheese); topping didn’t crisp; or oven temp too low. Sauté veggies well, press out moisture, bake until set.
Q: How do I know when the casserole is done?
Look for golden top, bubbling edges, center set (not jiggly). A knife or toothpick inserted near center should come out mostly clean (maybe a few moist crumbs but not liquid).
Q: Is this good for feeding guests / potlucks?
Absolutely! It can be made ahead or frozen, travels well, pairs with many mains.
Sample Recipe Card (Printable)
Zucchini, Squash & Corn Casserole
- Servings: 8
- Prep Time: ~15‑20 minutes
- Cook Time: ~45‑50 minutes
- Total Time: ~1 hour (including resting)
Ingredients
- 1½ lb yellow squash, thinly sliced
- 1½ lb zucchini, thinly sliced
- 2 cups diced sweet onion
- 2 cloves garlic, minced
- 3 cups corn kernels
- 1½ cups shredded white cheddar cheese
- ½ cup sour cream
- ½ cup mayonnaise
- 2 eggs, lightly beaten
- ¼ cup butter, divided
- Salt 1 tsp; pepper 2 tsp (adjust to taste)
- 1½ cups fresh breadcrumbs, divided
- 1 cup Parmesan or Asiago cheese, grated, divided
Instructions
- Preheat oven to 350°F (175°C). Grease 9×13‑inch baking dish.
- Melt 2 Tbsp butter; sauté onion until soft, add garlic, then squash & zucchini. Cook until tender (≈8‑10 min). Add corn, stir, remove from heat.
- In bowl, whisk sour cream, mayonnaise, eggs, cheddar, salt, pepper. Fold in veggies + half breadcrumbs + half Parmesan.
- Spread into dish. Melt remaining butter; mix with remaining breadcrumbs + remaining Parmesan, sprinkle on top.
- Bake 45‑50 min until top golden and edges bubbling. Rest a few minutes before serving.
Final Thoughts
This Zucchini, Squash & Corn Casserole is a perfect example of comfort food that doesn’t feel heavy — it has fresh veggies, creamy cheese, great textures, and a cheesy, buttery crust. It works all summer and into early fall, and is versatile enough for adaptation.
