The smell of this sauce as it’s simmering is pure autumn heaven; fill your home with the scent of fall and prepare to go back for seconds — maybe even thirds.
1. Heat butter in a 5- to 6-quart heavy pot over moderately high heat until foam subsides, then add sage and cook until fragrant (about 15 seconds).
2. Add cubed squash, diced onions, water, salt and pepper and simmer, uncovered, stirring occasionally, until squash is very tender and water has reduced considerably (about 10-15 minutes).
3. Remove from heat and extract the sage leaves. If you have an immersion blender, puree mixture right in the pot. If you don’t, transfer mixture to a food processor or blender and puree until smooth. Add a grating of fresh nutmeg if you wish. The sauce should be thick enough to coat the back of a spoon (if too thin, simmer over low heat until it thickens).
4. While squash mixture simmers, cook pasta according to package directions. When draining, reserve 1 cup of the pasta cooking water and set aside.
5. Place pasta in a serving bowl. Toss with enough butternut-sage sauce to coat nicely. If necessary, add a little bit of the reserved pasta water to thin it out. Serve pasta with freshly grated Parmigiano-Reggiano cheese.
Makes 3-4 servings.