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 (see notes below); 1/4 teaspoon black pepper; 1/2 teaspoon dried thyme; 1 tablespoon fresh garlic (minced); 1 cup cheddar cheese (sharp, shredded )

Jump to Recipe

This cheesy spaghetti squash casserole is made with sour cream and cheddar. It's great as a side dish but is substantial and filling enough to serve as a meatless main course. The leftovers are excellent, and you can quickly reheat them in the microwave.

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

You'll only need a few simple ingredients to make this casserole. The exact measurements are included in the recipe card below. Here's an overview of what you'll need:

Spaghetti squash: I use a 3-pound squash in this recipe.
Egg: I use large eggs in most of my recipes, this one included.
Sour cream: Please use full-fat sour cream.
Minced garlic: Mince it yourself, or use the stuff that comes in a jar.
To season: Kosher salt, black pepper, and dried thyme.
Shredded sharp cheddar: Extra-sharp cheddar is even better. It's more flavorful.

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 to the mixture.
You can use different cheeses. Provolone, gruyere, and gouda are excellent options.
Use softened cream cheese instead of sour cream.
You can use dried oregano instead of thyme. Both work equally well.
Substitute a teaspoon of garlic powder for the minced garlic.

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

Instructions

Scroll down to the recipe card for detailed instructions. Here are the basic steps for making this recipe:

Your first step is to cook the squash. I usually microwave it, but you can also bake it in the oven. 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 until uniform.

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.

Expert Tips

Cutting or Scooping the Casserole

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.

You Can Double This Recipe

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, as shown in the photo below:

Spaghetti squash casserole is baked in a 3.5-quart baking dish.

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:

Two spaghetti squashes in the microwave.

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.

Can I substitute Greek yogurt for sour cream?

I don't recommend that. I tried it, and it wasn't as good.

Serving Suggestions

This casserole makes an excellent side dish but is also substantial and filling enough to serve as a meatless main dish.

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 Leftovers

You can keep the leftovers in a sealed container in the fridge for up to four days. I like to 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 plastic wrap layer 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: