Bring a large pot of salted water to a boil over high heat. Add the pasta and cook according to the package directions.
Drain the pasta and return to the pot.
Stir the butter, sweet potato puree, cheese, and milk into the pasta and season with salt and pepper.
Serve the pasta warm.
Preheat the oven to 400°F.
Using a knife, poke a few holes in the potato. Place in a pie plate or on a baking sheet and bake for about 1 hour, or until very soft.
Discard the peel and, using a fork, mash the potato until very smooth (or blend in a blender) before using.
