Place the stock in a pot and bring to a gentle simmer. Heat the oil in another pot over medium heat. Add the squash and onion and cook, stirring, 5 minutes. Add the rice and cook, stirring constantly, 2 minutes more. Pour in the wine and simmer until it almost entirely evaporates. Add 1/2 of the simmer stock all at once. Adjust the heat so that the liquid gently bubbles over the entire surface. Cook the rice, stirring often, until it has absorbed the stock, about 15 minutes. Add the remaining stock 1/2 cup at a time, making the next addition when the rice has almost absorbed the last, and cook until rice is tender. (Be careful not to add to too much stock at the end of cooking time because the rice should be naturally creamy, not swimming in broth). Stir in the cheese and the sage. Remove from heat, cover and let stand 5 minutes. Stir in the parsley and serve with more freshly grated Parmigiano-Reggiano at the table.
Note: Risotto, which is short to medium grained, can be found in the aisle rice is sold.
Recipe Options: Use other types of squash such as banana or Hubbard instead of butternut. If you're not vegetarian, you can use chicken stock instead of vegetable.