Ingredients:

  • 1 medium spaghetti squash (about 2.5–3 lb / 1.1–1.4 kg)
  • 1 tablespoon olive oil (15 ml)
  • 1/2 teaspoon fine salt (2.5 g)
  • 1/4 teaspoon black pepper (freshly ground)
  • 2 tablespoons unsalted butter (28 g)
  • 2 tablespoons all-purpose flour (16 g)
  • 1 1/2 cups whole milk (360 ml) — can use 2% for lower fat
  • 1/2 cup heavy cream (optional for extra richness) (120 ml) — optional; if omitted, use 2 cups milk total (480 ml)
  • 1 cup sharp cheddar, shredded (4 oz / 113 g)
  • 1/2 cup grated Parmesan (2 oz / 50 g), plus 2 tablespoons reserved for topping
  • 1/2 cup shredded mozzarella (optional for extra melt) (2 oz / 56 g)
  • 1/2 teaspoon Dijon mustard (optional, for depth)
  • 1/4 teaspoon garlic powder (or 1 small clove minced garlic, sautéed)
  • 1/4 teaspoon ground black pepper
  • 1/2 teaspoon fine salt (adjust to taste)
  • 1 large egg, beaten (optional — helps set the casserole; keep refrigerated until needed)
  • 1/2 cup panko breadcrumbs (about 50–60 g)
  • 1 tablespoon unsalted butter, melted (14 g)
  • 2 tablespoons grated Parmesan (about 10 g)
  • Optional: 1 teaspoon chopped fresh parsley for garnish
  • Optional add-ins: 1 small onion, finely diced and sautéed (about 1 cup cooked); 4–6 oz cooked bacon or pancetta, chopped (115–170 g); 8 oz cooked Italian sausage, crumbled (225 g); 1 cup fresh spinach, wilted and squeezed dry

Instructions:

  1. Preheat oven to 400°F (200°C). Line a rimmed baking sheet with parchment paper or foil if desired.
  2. Cut the spaghetti squash in half lengthwise (stabilize squash and cut slowly; if very firm, microwave whole for 1–2 minutes to soften). Scoop out seeds and strings.
  3. Brush cut sides with olive oil and season with 1/2 teaspoon salt and 1/4 teaspoon pepper. Place cut-side down on the prepared baking sheet and roast 40–50 minutes, until a knife easily pierces and a fork pulls out long, tender strands.
  4. While squash roasts, make the cheese sauce: melt 2 tablespoons butter in a saucepan over medium heat. Whisk in 2 tablespoons flour to make a roux and cook 1–2 minutes without browning.
  5. Slowly whisk in milk (and cream if using). Bring to a gentle simmer and cook 4–6 minutes until sauce thickens and coats the back of a spoon. Reduce heat to low and stir in Dijon, garlic powder, 1/4 teaspoon black pepper, and 1/2 teaspoon salt.
  6. Off heat, whisk in cheddar, Parmesan, and mozzarella (if using) a handful at a time until smooth. If using the egg, temper it by whisking a few tablespoons of hot sauce into the beaten egg, then whisk the egg mixture back into the sauce. Keep warm.
  7. When squash is cool enough to handle, use a fork to scrape the flesh into long strands into a large bowl. Taste and adjust salt as needed.
  8. Pour the cheese sauce over the scraped squash strands and fold gently to combine. Fold in any cooked optional add-ins (sautéed onion, bacon, sausage, wilted spinach) if using. Transfer mixture to an 8x8- or 9x13-inch ovenproof baking dish, smoothing the top.
  9. Make the topping by mixing panko breadcrumbs with melted butter and 2 tablespoons grated Parmesan. Sprinkle evenly over the casserole top. Optionally sprinkle a little extra shredded cheddar over the panko for more browning.
  10. Bake at 375°F (190°C) for 18–25 minutes, until the top is golden and the sauce is bubbling at the edges. For a deeper brown crust, finish 1–2 minutes under a hot broiler—watch carefully to avoid burning.
  11. Let the casserole rest 5–10 minutes to set slightly. Garnish with chopped parsley if desired and serve warm.