Simple Yellow Squash Casserole with Mayonnaise

Here is my favorite yellow squash casserole recipe, with tender sliced squash, a creamy mayonnaise and sour cream base, sharp cheddar cheese, and a buttery cracker topping.

This casserole is what I make whenever I have too much yellow squash from the garden or farmer’s market. It’s become a regular side dish at our dinner table, and my kids actually ask for seconds of their vegetables. Can’t beat that, right?

What Kind of Yellow Squash Should I Use?

Any yellow squash you find at the grocery store will work great for this casserole. Summer squash and yellow crookneck squash are the most common varieties, and they’re pretty much interchangeable in this recipe. Look for squash that feels firm to the touch and has smooth, unblemished skin – avoid any that feel soft or have dark spots. Smaller to medium-sized squash tend to have fewer seeds and a sweeter flavor than the really large ones, so grab those if you have the option.

Options for Substitutions

This casserole is pretty forgiving when it comes to swapping ingredients:

• Yellow squash: You can easily swap yellow squash with zucchini, or use a mix of both. They cook the same way and have similar textures, so no changes needed to the recipe.
• Mayonnaise: If you’re not a mayo fan, Greek yogurt works as a substitute. Keep in mind it’ll make the casserole slightly tangier and a bit less rich, but it still tastes great.
• Sour cream: Plain Greek yogurt or even cream cheese (softened) can replace sour cream. If using cream cheese, you might need to thin it with a tablespoon or two of milk to get the right consistency.
• Cheddar cheese: Feel free to use Monterey Jack, Colby, or a Mexican cheese blend instead. Gruyere also works if you want something fancier.
• Ritz crackers: Crushed butter crackers like Club crackers work well, or you can use panko breadcrumbs mixed with 2 tablespoons of melted butter for a similar crunchy topping.

Watch Out for These Mistakes While Baking

The biggest mistake people make with squash casserole is skipping the pre-cooking step, which releases excess moisture from the squash – if you add raw squash directly to the baking dish, you’ll end up with a watery casserole instead of a creamy one.

Make sure to let the cooked squash cool for the full 5-10 minutes before mixing in the mayo, sour cream, and cheese, otherwise the heat will cause the cheese to clump and the dairy to separate.

To keep your cracker topping crispy instead of soggy, wait until the last 10-15 minutes of baking to add it, or toss the crushed crackers with a tablespoon of melted butter before sprinkling them on top.

Finally, resist the urge to skip the resting time after baking – those 5-10 minutes allow the casserole to firm up so it doesn’t fall apart when you scoop it out.

What to Serve With Yellow Squash Casserole?

Yellow squash casserole is a Southern side dish that pairs beautifully with just about any protein you’re grilling or roasting. I love serving it alongside baked chicken, grilled pork chops, or even a simple roasted turkey breast for a comforting weeknight dinner. Since the casserole is rich and creamy, it’s nice to balance it out with something fresh like a crisp coleslaw or a simple cucumber and tomato salad. For a full Southern-style spread, add some cornbread and green beans to round out the meal.

Storage Instructions

Store: Keep any leftover squash casserole covered tightly with foil or in an airtight container in the fridge for up to 4 days. The crackers on top might lose some crunch, but the casserole itself stays creamy and delicious.

Freeze: This casserole freezes pretty well for up to 2 months. I’d recommend freezing it before adding the cracker topping, then add fresh crushed crackers when you’re ready to reheat. Wrap it tightly in plastic wrap and then foil to prevent freezer burn.

Reheat: Warm it up in a 350°F oven for about 20 minutes until heated through, or microwave individual portions for 2-3 minutes. If the top needs crisping up, just pop it under the broiler for a minute or two.

Estimated Nutrition

Estimated nutrition for the whole recipe (without optional ingredients):

• Calories: 970-1100
• Protein: 22-27 g
• Fat: 68-78 g
• Carbohydrates: 75-90 g

Ingredients

For the squash mixture:

• 3 lb yellow squash (cut into 1/2-inch thick slices)
• 1 onion (finely diced into 1/4-inch pieces)
• 3/4 tsp salt
• 1 1/2 tsp onion powder
• 1 1/2 tsp garlic powder
• 1/2 tsp black pepper
• 1/2 tsp cayenne pepper
• 1/3 cup mayonnaise
• 1/3 cup sour cream
• 1 1/4 cups sharp cheddar cheese
• 1/2 tsp fresh thyme leaves

For the topping:

• 20 crackers (crushed into small, coarse crumbs)
• 2 tbsp unsalted butter, melted

Step 1: Prepare Mise en Place and Season the Squash

• 3 lb yellow squash, sliced into 1/2-inch thick rounds
• 1 onion, finely diced
• 3/4 tsp salt
• 1 1/2 tsp onion powder
• 1 1/2 tsp garlic powder
• 1/2 tsp black pepper
• 1/2 tsp cayenne pepper
• 20 crackers, crushed into coarse crumbs

Slice the yellow squash into 1/2-inch thick rounds and finely dice the onion into 1/4-inch pieces.

In a small bowl, combine the salt, onion powder, garlic powder, black pepper, and cayenne pepper—mixing them together ensures even seasoning distribution throughout the dish.

Crush the crackers into small, coarse crumbs (you want some texture, not fine breadcrumbs) and set aside.

I like to do all my prep work first so I can focus on the cooking without interruption.

Step 2: Cook the Squash and Onion Until Tender

• 3 lb yellow squash, sliced
• 1 onion, finely diced
• spice mixture from Step 1

Heat a large skillet over medium-high heat and add the sliced squash and diced onion.

Sprinkle with the spice mixture from Step 1 and cook for 10 minutes, stirring occasionally, until the squash is tender and begins to release its moisture.

The squash will soften and the onion will become translucent as it cooks.

Transfer the cooked mixture to a bowl and let it cool for 5-10 minutes so it’s manageable to work with.

Step 3: Build the Creamy Casserole Base

• cooked squash mixture from Step 2
• 1/3 cup mayonnaise
• 1/3 cup sour cream
• 1 1/4 cups sharp cheddar cheese
• 1/2 tsp fresh thyme leaves

Once the squash mixture has cooled slightly, stir in the mayonnaise, sour cream, and sharp cheddar cheese until everything is evenly combined.

Gently fold in the fresh thyme leaves, which will add a subtle herbaceous note to balance the richness.

I find that stirring in the creamy ingredients while the squash is still warm helps them distribute more smoothly and creates a cohesive sauce.

Step 4: Assemble and Top the Casserole

• squash and cheese mixture from Step 3
• buttered cracker crumbs

Preheat your oven to 375°F.

Grease a 9×13 inch baking dish lightly with butter or cooking spray, then transfer the squash mixture into the prepared dish and spread it evenly.

Toss the crushed crackers from Step 1 with the melted butter until they’re lightly coated, then sprinkle them evenly over the top of the casserole.

The buttered crackers will toast and create a golden, crunchy crust.

Step 5: Bake and Rest the Casserole

Place the casserole in the preheated 375°F oven and bake for 30 minutes, until the top is golden brown and the filling is hot throughout.

Remove from the oven and let it rest for 5-10 minutes before serving—this allows the casserole to set slightly and makes it easier to portion without falling apart.

Simple Yellow Squash Casserole with Mayonnaise

Delicious Simple Yellow Squash Casserole with Mayonnaise recipe with step-by-step instructions.

Print Recipe Pin Recipe

Prep Time 20 minutes mins

Cook Time 40 minutes mins

Total Time 1 hour hr

Servings: 6 servings

Calories: 1035

Ingredients Method

Ingredients

  

For the squash mixture:

• 3 lb yellow squash (cut into 1/2-inch thick slices)
• 1 onion (finely diced into 1/4-inch pieces)
• 3/4 tsp salt
• 1 1/2 tsp onion powder
• 1 1/2 tsp garlic powder
• 1/2 tsp black pepper
• 1/2 tsp cayenne pepper
• 1/3 cup mayonnaise
• 1/3 cup sour cream
• 1 1/4 cups sharp cheddar cheese
• 1/2 tsp fresh thyme leaves

For the topping:

• 20 crackers (crushed into small, coarse crumbs)
• 2 tbsp unsalted butter, melted

Method

 

1. Slice the yellow squash into 1/2-inch thick rounds and finely dice the onion into 1/4-inch pieces. In a small bowl, combine the salt, onion powder, garlic powder, black pepper, and cayenne pepper—mixing them together ensures even seasoning distribution throughout the dish. Crush the crackers into small, coarse crumbs (you want some texture, not fine breadcrumbs) and set aside. I like to do all my prep work first so I can focus on the cooking without interruption.
2. Heat a large skillet over medium-high heat and add the sliced squash and diced onion. Sprinkle with the spice mixture from Step 1 and cook for 10 minutes, stirring occasionally, until the squash is tender and begins to release its moisture. The squash will soften and the onion will become translucent as it cooks. Transfer the cooked mixture to a bowl and let it cool for 5-10 minutes so it's manageable to work with.
3. Once the squash mixture has cooled slightly, stir in the mayonnaise, sour cream, and sharp cheddar cheese until everything is evenly combined. Gently fold in the fresh thyme leaves, which will add a subtle herbaceous note to balance the richness. I find that stirring in the creamy ingredients while the squash is still warm helps them distribute more smoothly and creates a cohesive sauce.
4. Preheat your oven to 375°F. Grease a 9x13 inch baking dish lightly with butter or cooking spray, then transfer the squash mixture into the prepared dish and spread it evenly. Toss the crushed crackers from Step 1 with the melted butter until they're lightly coated, then sprinkle them evenly over the top of the casserole. The buttered crackers will toast and create a golden, crunchy crust.
5. Place the casserole in the preheated 375°F oven and bake for 30 minutes, until the top is golden brown and the filling is hot throughout. Remove from the oven and let it rest for 5-10 minutes before serving—this allows the casserole to set slightly and makes it easier to portion without falling apart.