Cook the macaroni according to package directions until al dente. Drain and set aside.
In a large pot over medium heat, melt the butter. Whisk in the flour and cook for 1-2 minutes until it forms a paste.
Gradually whisk in the milk, stirring constantly to prevent lumps. Cook until the mixture thickens, about 3-5 minutes.
Stir in the pumpkin puree, garlic powder, nutmeg, salt, and pepper until well combined.
Remove from heat and add the shredded cheese, stirring until completely melted and smooth.
Add the cooked macaroni to the cheese sauce and stir until evenly coated.
For a crispy topping, transfer to a baking dish, sprinkle with panko breadcrumbs, and broil for 2-3 minutes until golden. Serve immediately and watch it disappear!