Preheat your oven to 400°F (200°C). Carefully cut the spaghetti squash in half lengthwise and scoop out the seeds. Place the halves cut-side down on a baking sheet lined with parchment paper or foil. Roast for 30–40 minutes, until the flesh is tender and easily shredded with a fork. Let the squash cool slightly, then use a fork to scrape the inside into spaghetti-like strands.

While the squash cools, melt 2 tablespoons of butter in a large skillet over medium heat. Add the finely chopped onion and cook until soft and translucent, about 5 minutes. Stir in the minced garlic and sauté for another 30 seconds, just until fragrant.

Add the shredded spaghetti squash to the skillet with the onions and garlic. Reduce the heat to low and stir in the sour cream, mixing until everything is creamy and well-combined. Season with salt and pepper to your taste. Stir in 1 cup of shredded sharp Cheddar cheese and mix until fully melted and smooth.

Preheat your oven’s broiler. Transfer the creamy squash mixture into a greased 8×8-inch baking dish. Sprinkle the remaining 1/2 cup of Cheddar cheese evenly over the top. Broil for 2 to 4 minutes, watching closely, until the cheese is bubbly and golden brown.

Sprinkle chopped parsley over the top if desired. Serve warm, either as a comforting side dish or a light main course alongside your favorite protein.