Bring a large pot of salted water to a boil.

Add butternut squash and cook until soft. Remove with a slotted spoon and blend until smooth.

Add pasta to boiling water and cook according to package instructions for al dente. Reserve 1 cup of pasta water before draining.

Meanwhile, sauté leeks and garlic in butter over medium-low heat until soft and golden, about 5-6 minutes.

Add pureed butternut squash, season with salt and pepper, and add reserved pasta water to thin as needed.

Stir in parmesan cheese and sage, then mix in cooked pasta until well coated.

Serve with additional parmesan cheese on the side.