Cheesy Spaghetti Squash Casserole

CasseroleLow CarbVegetarianSpaghetti Squash

This Cheesy Spaghetti Squash Casserole is loaded with cheese, fresh sage, and roasted red peppers. This vegetarian casserole makes a rich, decadent main dish or the perfect vegetarian holiday side.

Photography Credit: Sally Vargas

This Spaghetti Squash Casserole was a big hit at a potluck recently where there were more than a few vegetarians around the table, and it would be a welcome addition during the holidays.

What’s not to love about a tender squash, creamy cheese, fresh sage, and red peppers?

WHAT IS SPAGHETTI SQUASH?

Just to be clear, spaghetti squash is a vegetable! It looks a bit like a large, yellow melon, but when you cut it open, pale yellow spaghetti-like strands lurk under the seeds. You could say spaghetti squash is kind of cool.

But let’s be perfectly honest. It’s also a bit on the bland side, in the way zucchini is bland, but with a totally different texture.

Unlike the bold, intense flavors of butternut or acorn squash, spaghetti squash is like a blank canvas, waiting to be infused with flavors. It’s a great alternative for ‘squash haters’—they will immediately be converted when they taste this cheesy casserole.

HOW TO CUT AND COOK A SPAGHETTI SQUASH

Spaghetti squash is a member of the gourd family, which means the outer shell is very tough. I use a few tricks to make cutting the squash easier. When you are finished cutting it, you want two long halves.

  • On a cutting board, set the squash on a folded dishtowel to keep it stable.
  • Hold the squash steady with one hand, and insert a large chef’s knife into the center of the squash the long way, and push it down to cut the squash in half.
  • If you find you have trouble cutting the squash into even halves, try first scoring a line or making several deep slits with your knife around the squash (from end to end) and then use that as a guide for cutting.
  • Once you have two halves, scrape out the seeds with a sharp-edged spoon and discard (or roast) the seeds. Place the halves with the cut sides down on a parchment lined baking sheet and bake.

MAKE AHEAD TIPS FOR THIS CASSEROLE

OPTION 1: Prep the different components ahead of time.

  • You can prepare the components of the casserole (bake the squash, make the egg and cream mixture, cook the peppers and onions, grate the cheese) up to three days ahead of time and store each component separately in the refrigerator. Assemble and bake as directed in the recipe.

OPTION 2: Refrigerate the baked casserole.

  • Assemble and bake the casserole. When cooled to room temperature, cover with plastic wrap and refrigerate for up to three days. Reheat in a 350ºF oven for 20 minutes, or until the casserole is hot all the way through.

OPTION 3: Freeze the baked casserole.

  • Assemble and bake the casserole. When cooled to room temperature, cover with plastic wrap and then foil, and freeze for up to two months. Defrost in the refrigerator overnight and bake at 350ºF for 20 minutes, or until the casserole is hot all the way through.

NEED MORE VEGETARIAN RECIPES?

Cheesy Spaghetti Squash Casserole Recipe

  • Prep time: 1 hour
  • Cook time: 45 minutes
  • Yield: 6 to 8 servings

Ingredients

  • 1 tablespoon olive oil plus more for the baking dish
  • 1 spaghetti squash, about 3 pounds
  • 2 teaspoons salt
  • 1/2 teaspoon ground black pepper
  • 1 onion, finely chopped
  • 1 clove garlic, minced
  • 1/2 cup jarred roasted red peppers, thinly sliced
  • 2 tablespoons chopped fresh sage leaves
  • 3 eggs
  • 1 cup whole milk
  • 3 tablespoon flour
  • 1 1/2 cups (5 ounces) grated Jarlsberg or baby Swiss cheese
  • 1/2 cup (2 ounces) finely grated Parmesan

Special equipment:

Method

1 Preheat the oven to 425ºF. Line a baking sheet with parchment. Brush or spray a shallow 2-quart baking dish with oil.

2 Roast the squash: Cut the squash in half lengthwise and scrape out the seeds. Sprinkle with 1/4 teaspoon salt and 1/8 teaspoon pepper. Place on the baking sheet with the cut sides down. Bake for 30 to 40 minutes, or until the squash is tender when pierced with the tip of a paring knife.

Remove from the oven and turn the squash so the cut sides are facing up. Return the squash to the oven and bake for another 5 minutes to dry out any excess liquid. (The squash won’t necessarily look dry.) Remove and let cool.

3 Cook the other ingredients: In a large skillet set over medium heat, add 1 tablespoon of oil. Once the oil begins to shimmer, add the onions, 1/4 teaspoon salt, and 1/4 teaspoon pepper. Cook, stirring occasionally, for 5 minutes or until softened.

Stir in the garlic, red pepper slices, and sage. Cook and stir for another minute. Transfer to a large bowl.

4 Make the egg mixture: In a blender (immersion or countertop), pulse the eggs, milk, flour, 1/2 teaspoon salt and 1/8 teaspoon pepper 3 to 4 times, or until the mixture is smooth.

5 Mix it all together: With a fork, flake the squash strands into the bowl on top of the onions. Add 1 teaspoon salt and mix until combined. Add the egg mixture, grated Jarlsberg cheese, and 1/4 cup of the Parmesan to the squash. Stir to combine.

6 Bake the casserole: Transfer the squash mixture to the baking dish and sprinkle it with the remaining 1/4 cup Parmesan. Bake for 40 to 45 minutes.

7 Serve: Let rest for 10 to 15 minutes before serving as a side dish or a vegetarian main.

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Sally Vargas

Sally Pasley Vargas is a freelance writer and the author of three cookbooks (Food for Friends, The Tao of Cooking, Ten Speed Press, and The Cranberry Cookbook). She currently writes the column The Confident Cook for The Boston Globe along with seasonal recipes for the Wednesday Food Section.

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Cheesy Spaghetti Squash Casserole