Spaghetti Squash Au Gratin

The first time I made this, my husband actually thought it was pasta. He took three bites before pausing and asking why the 'spaghetti' tasted so much better than usual. That moment of watching someone realize comfort food can be healthy is pure kitchen magic.

I served this at my book club last winter, and we spent the first ten minutes just guessing what was in it. The conversation turned into this lovely debate about whether healthy food could actually taste indulgent. Watching everyone go back for seconds while feeling virtuous was the best kind of dinner party victory.

Ingredients

• 1 large spaghetti squash: Pick one that feels heavy for its size and has a firm, unblemished skin
• 2 tablespoons olive oil: Divide this for roasting the squash and sautéing the aromatics
• 1 small yellow onion: Finely chopped so it melts into the sauce without overwhelming the dish
• 2 cloves garlic: Minced fresh garlic makes such a difference here, dont skip it
• 1 cup shredded Gruyère cheese: This cheese melts into the most incredible velvety sauce
• 1/2 cup grated Parmesan cheese: Adds that salty, nutty depth that makes gratins irresistible
• 1/2 cup sour cream: The secret to making the sauce tangy and rich without using flour
• 2 tablespoons unsalted butter: Use this with the oil when cooking your onions for extra flavor
• 1/4 cup milk: Whole milk gives the best results, but 2 percent works fine too
• 1/2 teaspoon salt: Split between seasoning the squash and the final mixture
• 1/4 teaspoon ground black pepper: Freshly cracked makes all the difference
• 1/4 teaspoon ground nutmeg: Just a pinch adds this warm, subtle complexity
• 1 tablespoon chopped fresh parsley: The pop of green makes it look as good as it tastes

Instructions

Get your oven ready:

Preheat to 400°F and line a baking sheet with parchment paper for easy cleanup later

Prep the squash:

Cut it in half lengthwise, scoop out the seeds, then drizzle the cut sides with 1 tablespoon olive oil and season with salt and pepper

Roast until tender:

Place squash halves cut side down on the baking sheet and roast for 35 to 40 minutes until the flesh shreds easily with a fork

Sauté the aromatics:

While the squash roasts, heat the remaining olive oil and butter in a skillet over medium heat, cook the onion until soft and translucent, about 5 minutes, then add garlic for 1 minute more

Shred the squash:

Let the squash cool slightly, then use a fork to scrape the flesh into strands and place them in a large mixing bowl

Make the sauce mixture:

Add the cooked onion and garlic, sour cream, milk, half the Gruyère, half the Parmesan, nutmeg, salt, and pepper to the bowl, then mix until everything is well combined

Assemble the gratin:

Transfer the mixture to a greased 2 quart baking dish and top with the remaining Gruyère and Parmesan

Bake until golden:

Reduce the oven temperature to 375°F and bake for 20 to 25 minutes until the top is beautifully golden and bubbly

Finish and serve:

Garnish with chopped parsley right before serving, if you want that extra pop of color

Save

This dish has become my go to when friends announce they are eating low carb. Theres something so satisfying about watching someone who expects diet food take that first bite and suddenly relax. Food should never feel like punishment, and this gratin proves that beautifully.

Make It Your Own

I have played around with different cheeses, and sharp cheddar creates this completely different but equally delicious version. Fontina works wonderfully too, melting into these gorgeous puddles of creaminess throughout the dish.

Perfect Pairings

This gratin holds its own as a vegetarian main, but it also shines alongside roast chicken or pork. The richness calls for something bright and fresh on the side, like a simple green salad with vinaigrette.

Storage and Reheating

The leftovers reheat surprisingly well, which is rare for creamy dishes. I have learned to cover it with foil when reheating so the cheese does not dry out before the center is warm.

• Keep it covered in the refrigerator for up to 4 days
• Reheat at 350°F for about 15 minutes covered
• The flavors actually deepen and improve after a day or two

Save

There is nothing quite like pulling this bubbling, golden dish out of the oven on a chilly evening. It is comfort food that happens to be good for you, and that is the best kind of surprise.

Recipe FAQs

→ How do I know when the squash is properly roasted?

The squash is ready when the flesh is tender and easily pulls away from the skin in strands when scraped with a fork. This typically takes 35–40 minutes at 400°F. You should be able to pierce the skin easily with a fork.

→ Can I make this ahead of time?

Yes! Assemble the dish completely, cover tightly, and refrigerate for up to 24 hours before baking. You may need to add 5–10 extra minutes to the baking time if baking from cold. The flavors often meld together even better this way.

→ What other cheeses work well in this dish?

Sharp cheddar adds bold flavor, while fontina melts beautifully and offers a mild, nutty taste. Swiss cheese provides a classic gratin flavor, or try mixing multiple cheeses for complexity. Avoid fresh mozzarella as it releases too much moisture.

→ Is this suitable for keto diets?

This dish is naturally low-carb and keto-friendly, with about 19 grams of carbohydrates per serving. Most of the carbs come from the squash itself, which is much lower in carbs than potatoes used in traditional gratin.

→ How do I store leftovers?

Store in an airtight container in the refrigerator for 3–4 days. Reheat in the oven at 350°F for 15–20 minutes, or microwave individual portions. The texture remains surprisingly good upon reheating, especially in the oven.

→ Can I freeze this gratin?

Yes, freeze before or after baking. If freezing unbaked, thaw overnight in the refrigerator before baking as directed. Already-baked portions can be frozen for up to 2 months and reheated in a 350°F oven until hot throughout.