Cheesy Spaghetti Squash Casserole

Name: Cheesy Spaghetti Squash Casserole
Prep time: 15 min
Cook time: 40 min
Total time: 65 min
Ingredients: Olive oil cooking spray; 1 (3 pounds) raw spaghetti squash (or 2 1/2 cups cooked spaghetti squash; 450 grams); 1 large egg; 1/2 cup sour cream; 1 teaspoon Diamond Crystal kosher salt; 1/4 teaspoon black pepper; 1/2 teaspoon dried thyme; 1 tablespoon fresh garlic (minced); 1 cup cheddar cheese (sharp, shredded )

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This cheesy spaghetti squash casserole is great as a side dish, but is substantial and filling enough to serve as a meatless main course.

Spaghetti squash casserole is scooped out of the baking dish.

This casserole is cheesy, delicious, and easy to make. I started making it whenever I had leftover baked spaghetti squash or microwave spaghetti squash. But it's so good, I now make it whenever I get the chance. You can make it as written or add mix-ins and turn it into a complete meal. The possibilities are endless!

Ingredients and Substitutions

The ingredients needed to make a spaghetti squash casserole.

See the recipe card for exact measurements. Here are my comments on some of the ingredients.

Spaghetti squash: I use a 3-pound squash.
Sour cream: Please use full-fat sour cream. You can use softened cream cheese instead of sour cream.
To season: Kosher salt, black pepper, and dried thyme. You can use dried oregano instead of thyme. Both work equally well.
Shredded sharp cheddar: You can use different cheeses, including provolone, gruyere, and Gouda.

Variations

Add more veggies, such as ½ cup of sauteed spinach (drain it well), ½ cup of sauteed mushrooms, ¼ cup of sauteed onions, or ¼ cup of chopped green onions.
Add a cup of cooked and shredded grilled chicken breast (plus an extra ¼ cup of sour cream) and turn this casserole into a complete meal.
I sometimes add ½ cup of bacon bits.

Like all casserole recipes, this one is flexible and forgiving. So go ahead and experiment with your own additions!

Instructions

The detailed instructions and step-by-step photos are included in the recipe card. Here's a quick overview.

Cook the squash. Scoop out the pulp and seeds, and rake a fork back and forth to remove strands of the flesh into a bowl. Whisk an egg, sour cream, and spices in a bowl. Add the squash strands and shredded cheese and mix to combine.

Transfer the mixture to a greased baking dish and bake it until browned, for about 40 minutes, in a 400°F oven.

Let the casserole rest, then cut it into four squares and serve.

Recipe Tip

Thanks to the addition of egg, this casserole is sturdy enough to cut into squares, as shown in the photo below. If you'd like to omit the egg, increase the sour cream to ¾ cup and use a large spoon to scoop the casserole onto plates.

Lifting a slice of casserole out of the pan.

Here is the casserole served on a plate after it was cut into squares:

A square of spaghetti squash casserole is served on a plate.

Recipe FAQs

Should I add flour?

There's no need to add flour. The egg acts as a binder, and the sour cream adds substance and creaminess. The casserole's texture is excellent without any added starch.

Should I cook the spaghetti squash before adding it to the casserole?

Yes. You can bake it in the oven or microwave it. I prefer microwaving because it's easier and faster. Here are the recipes I typically use: microwave spaghetti squash or baked spaghetti squash.

Can I substitute Greek yogurt for sour cream?

I don't recommend that. I tried it, and it wasn't as good. Greek yogurt is less creamy and more tangy than sour cream.

Can I double the recipe?

Yes. When I serve this recipe to a larger group, I double this recipe and bake it in a 3.5-quart baking dish (such as a 9 X 13 baking dish) or Dutch oven. If you double the recipe, you can microwave the two squashes at the same time. Microwave them for six minutes on the first side, six more minutes on the second, and then flip them again and microwave for six more minutes or until they are soft.

Serving Suggestions

This casserole makes an excellent side dish but is also substantial and filling enough to serve as a meatless main course. I usually serve it as a side dish, and since I bake it in a 400°F oven, I like to serve it with a main dish that I can cook in the same oven, such as:

Storing and Using the Leftovers

You can keep the leftovers in a sealed container in the fridge for up to four days. I keep them in a glass food storage container, as shown in the image below:

Leftover spaghetti squash casserole is kept in a glass food storage container.

You can also freeze this casserole. Allow it to cool completely, then wrap it in a layer of plastic wrap and then foil. It can be frozen for up to three months. Reheat the leftovers gently in the microwave at 50% power. Here's a recent dinner plate I made with reheated spaghetti squash casserole, oven-baked ribs, and pickled okra: