Cook pasta in a large pot of heavily salted water until al dente. Reserve 1 ½ cups pasta water and drain.
Heat olive oil in a large skillet over medium heat. Add garlic and cook until aromatic, 1 minute. Add pumpkin puree, 1 cup of reserved pasta water, whisking to combine until sauce is combined and glossy. Add half and half and stir to combine. Add remaining pasta water if needed. Season with salt, pepper, and nutmeg.
Notes
Storage: Store any leftovers in an airtight container. They will last about 4-5 days in the fridge.