Creating Cheesy Spaghetti Squash Au Gratin is simple when you follow these detailed steps:

1. Preheat the Oven: Preheat your oven to 375°F (190°C).
2. Prepare Spaghetti Squash: Cut the spaghetti squash in half lengthwise. Scoop out the seeds using a spoon.
3. Roast the Squash: Drizzle the cut sides with olive oil and season with salt. Place the squash cut-side down on a baking sheet. Roast for 30-35 minutes or until tender.
4. Scoop Flesh: Once cooled, use a fork to scrape the flesh of the squash into spaghetti-like strands and transfer to a large bowl.
5. Prepare the Cheese Mixture: In a separate bowl, combine the cheddar cheese, mozzarella cheese, Parmesan cheese, heavy cream, minced garlic, thyme, salt, and pepper. Stir until well combined.
6. Combine Mixtures: Fold the cheese mixture into the spaghetti squash until the squash is well coated.
7. Transfer to Baking Dish: Spread the cheesy spaghetti squash mixture evenly in a greased baking dish.
8. Add Topping: If using breadcrumbs, sprinkle them over the top for a crunchy crust.
9. Bake: Place the dish in the preheated oven and bake for 20-25 minutes or until the top is golden and bubbly.
10. Cool and Serve: Remove from the oven, letting it cool for about 5-10 minutes. Garnish with fresh parsley before serving.

By meticulously following these steps, you’ll successfully create a delicious Cheesy Spaghetti Squash Au Gratin that’s both comforting and flavorful.