Warm the broth in a small saucepan over low heat.
Meanwhile, heat the oil in a large saucepan over medium heat. Add the onion, salt, and pepper and cook for 4 minutes. Add the sage and cook for 1 minute. Add the squash and garlic and cook until the squash begins to soften, about 3 minutes. Add the rice and cook, stirring constantly, for 3 minutes. Add the wine and cook, stirring frequently, until the liquid is absorbed, about 3 minutes. Add the broth, 1/2 cup at a time, stirring occasionally and waiting until it is absorbed before adding more. It should take about 30 minutes for all the broth to be absorbed. Remove from heat and stir in the Parmesan. Spoon into individual bowls.
Tip: To grate a butternut squash, rub it against the large holes of a box grater, or roughly chop it, then pulse it in a food processor.