Melt the butter in a dutch oven, then add the garlic and onion
Cook over medium high heat for 8 - 10 minutes, stirring often, until the onion is softened
Add the milk, pumpkin, heavy cream, and sage, and cook over medium low heat, stirring often, until it begins to thicken, around 10 - 15 minutes
Add the parmesan cheese in and stir (this will thicken it more)
Cook the rigatoni or other pasta to al dente, drain, and add to the pumpkin sauce
Salt to taste (I used 1 teaspoon)
Serve topped with additional parmesan cheese