1) Preheat oven to 350 degrees F. Cut squash in half down the middle. Roast the squash, cut-side up, for 50-60 minutes until the flesh is fork tender.
2) When squash is roasted, remove from oven and let cool briefly. Then scrape out flesh with a fork and measure out amount for recipe and place in a bowl. Mash the squash well.
3) Meanwhile, peel and chop 2 Russet potatoes. Boil the potatoes in salted water for 10-12 minutes until they are really tender. Then mash the potatoes and measure out amount for recipe. Add to the bowl with the squash.
4) Let the squash and potato mixture cool for a few minutes and then stir in egg, seasonings, cheese, and flour last. Mix dough with your hands until it’s combined, but not sticky. Depending on how moist the squash and potato was, you might need to add more flour.
5) Cut dough into quarters and roll out a quarter at a time on a floured, clean surface. Roll it out into a long rope about 1/2-inch in diameter. Then cut the gnocchi into 1/2 inch dumplings. Use a fork to press some depressions into each gnocchi. Then add the shaped gnocchi to a baking sheet covered with flour. Repeat with all the dough until your gnocchi are done.
6) At this point you can freeze the gnocchi on the baking sheet and then transfer them to a freezer-safe bag or cook them immediately in salted, simmering water for 5-6 minutes. The gnocchi might not be cooked through even after floating.
7) To make sauce for one serving of gnocchi (one quarter of the dough), add two tablespoons of butter to a small skillet over medium heat with about a teaspoon of minced sage (one big leaf). Let the butter melt and bubble for a minute or two. Then add boiled gnocchi to the skillet. Let cook, undisturbed for a few minutes until gnocchi start to crisp.
8) Add 1-2 tablespoons of pasta cooking water to the skillet to form a light sauce. Swirl to combine butter, pasta water, and pasta.
9) Serve gnocchi right away garnished with Parmesan cheese.