Boil the macaroni in a large pot of salted water according to package directions until al dente, then drain and set aside.

Melt the butter in a medium saucepan over medium heat.

Whisk in the flour and cook for approximately 60 seconds to form a blond roux, ensuring the raw flour scent is dissipated.

Gradually stream in the milk while whisking constantly to prevent lump formation, then simmer until the sauce thickens and coats the back of a spoon.

Whisk in the pumpkin puree, garlic powder, nutmeg, salt, and black pepper until the mixture is homogenous.

Reduce the heat to low and fold in the shredded cheddar cheese in batches, stirring until the sauce is smooth and the cheese is fully emulsified.

Combine the cooked macaroni with the pumpkin cheese sauce, tossing until each noodle is evenly coated.

Serve immediately at an internal temperature of at least 140°F (60°C).