Bring a large stockpot of generously salted water to a rolling boil. Add the rigatoni or penne and cook according to package directions until al dente.
Reserve 1/2 cup (120ml) of the starchy pasta water before draining. Drain the pasta in a colander and set aside.
Melt the butter in a large skillet over medium heat. Once the foam begins to subside, add the sage leaves and cook for 2 to 3 minutes, swirling often, until the butter turns golden brown and the sage crisps.
Use a slotted spoon to remove the sage leaves to a paper towel-lined plate, leaving the browned butter in the pan.
Reduce the heat to medium-low and add the minced garlic to the browned butter. Cook for 30 seconds, stirring constantly, until fragrant but not browned.
Whisk in the canned pumpkin puree until smooth. Add the reserved pasta water, nutmeg, salt, and pepper, whisking until the sauce is uniform.
If using heavy cream, stir it in now and simmer for 1 to 2 minutes until the sauce thickens slightly.
Add the drained pasta directly to the skillet with the sauce. Toss with tongs until every piece is coated.
Stir in the grated parmesan cheese and toss again until melted and glossy. Taste and adjust salt, pepper, or nutmeg as needed.
Divide the pasta among four bowls. Top each bowl with the crispy sage leaves and toasted pine nuts or pepitas, if using. Finish with an extra grating of parmesan cheese.