Preheat your oven to 200°C (400°F). Toss pumpkin chunks with olive oil, salt, and pepper, then spread them evenly on a baking sheet. Roast for 25-30 minutes until caramelized and tender, filling your kitchen with a warm, sweet aroma.
While the pumpkin roasts, bring a large pot of salted water to a boil. Cook the pasta until just al dente, about 8 minutes, then drain and set aside.
In a saucepan, melt the butter over medium heat. Add the flour and whisk constantly for about 1 minute until the mixture turns a light golden color and smells slightly nutty.
Gradually pour in the milk, whisking continuously to prevent lumps. Keep whisking until the sauce thickens and begins to bubble gently, about 5 minutes.
Stir in the grated cheddar cheese, roasted pumpkin puree, ground nutmeg, and season with salt and pepper. Continue whisking until the cheese melts and the sauce is smooth, with a velvety texture.
Combine the cooked pasta with the cheese and pumpkin sauce, folding gently to coat all the noodles evenly.
Transfer the pasta mixture to a baking dish and spread it out evenly. Bake uncovered for 15 minutes until bubbly and the top turns golden brown.
Remove from the oven and let it rest for a few minutes. The dish should be bubbling, with a slightly crispy top and creamy interior.
