Melt half of the butter in a large skillet over medium-high heat and cook the onion until tender.
While the onion is cooking, prepare the butternut squash. Peel the squash, cut it in half, and scoop out the seeds (a grapefruit spoon works well for this). Chop it into half inch cubes.
To the onions, add crushed red pepper and the butternut squash. Cook for 2-3 minutes and then add the rice. Toast the grains slightly. This will take only a few minutes.
Once the grains are toasted, it's time to start adding the broth. Turn down the heat to medium. Add a ladle full of the simmering broth at a time, waiting until almost all the liquid is absorbed to add more. Stir every time more liquid is added. Make sure the pan doesn't get completely dry because the rice will burn quickly if there is no liquid. Don't worry about using every drop of the broth, just use as mush as you need. It will be done when the rice is tender and creamy. It takes about 15 minutes.
Turn off the heat and stir in the remaining butter, sage and cheese.