01 - Preheat oven to 400°F. Line a baking sheet with parchment paper and arrange squash cubes evenly. Roast for 30 to 40 minutes until tender and caramelized.
02 - Place peeled and quartered potato in a pot of salted water. Bring to a boil and simmer 15 to 20 minutes until fork-tender. Drain thoroughly.
03 - Pass roasted squash and boiled potato through a potato ricer or mash until smooth. Spread the mash on a tray to cool slightly.
04 - In a large bowl, combine the cooled mash with Parmesan, salt, pepper, nutmeg if using, and beaten egg. Stir gently to blend.
05 - Gradually add flour to the mixture, stirring until a soft, slightly sticky dough forms. Use only enough flour for workable consistency.
06 - Transfer dough to a floured surface, divide into four portions. Roll each into long ropes about 0.75 inches thick. Cut into 1-inch pieces and optionally shape ridges using a fork or gnocchi board.
07 - Bring a large pot of salted water to a boil. Cook gnocchi in batches until they float to the surface, approximately 2 to 3 minutes. Remove with a slotted spoon.
08 - Melt butter in a skillet over medium heat. Add sage leaves and cook until aromatic. Toss cooked gnocchi in the sage butter to coat evenly.
09 - Plate gnocchi immediately, garnished with extra Parmesan cheese and fresh sage leaves if desired.