Fill a large pot with water and set it over high heat to bring it to a boil.

While the water heats, finely chop the onion, mince the garlic, and slice 6 of the sage leaves into thin strips. Leave the other 6 sage leaves whole for the finish.

When the water reaches a full boil, add the kosher salt.

Add the rigatoni to the boiling water and stir right away so it does not stick together. Cook it until tender with a slight bite in the center, 10 to 12 minutes.

Set a large skillet over medium heat and add the butter.

Put the 6 whole sage leaves into the melted butter. Cook them for 30 to 45 seconds, until they look darker and crisp. Transfer them to a small plate.

Add the chopped onion to the skillet. Cook it for 4 to 5 minutes, stirring often, until soft and lightly golden.

Add the minced garlic and the sliced sage to the skillet. Stir for about 30 seconds, just until fragrant.

Spoon the pumpkin puree into the skillet. Stir it into the onion mixture and cook for 2 minutes, until the puree looks a little darker and no longer raw-looking.

Pour the heavy cream into the skillet. Stir until the sauce is smooth and fully combined.

Lower the heat to low and stir in 3/4 cup of the grated Parmesan. Keep stirring until the cheese melts into the sauce.

When the rigatoni is ready, scoop 1 1/2 cups of the pasta water out of the pot and set it aside.