In a large pot, combine the macaroni, broth, milk, and pumpkin puree. Stir well to mix.
Place the pot over medium-high heat and bring the mixture to a boil, stirring frequently to prevent the pasta from sticking.
Once boiling, reduce the heat to low and simmer, stirring often, until the pasta is tender and the liquid has thickened, about 8-10 minutes.
Remove the pot from the heat and stir in the butter until melted.
Add the shredded cheese, garlic powder, nutmeg, salt, and pepper. Stir until the cheese is fully melted and the sauce is smooth.
Taste and adjust seasonings as needed. If desired, add a pinch of cayenne for extra warmth.
Let the mac and cheese stand for a few minutes to thicken before serving. It will continue to thicken as it cools.