Heat a large saucepan over medium heat, add broth and bring to a very low simmer.
Heat a large saute pan over medium heat. Add olive oil, butternut squash and onion. Cook, stirring frequently, until the edges of squash soften and onion becomes translucent, about 5 minutes.
Add garlic and cook another minute until garlic is very fragrant. Add arborio rice and salt, stir to coat the rice and slightly toast, about one minute. The risotto will be very dry at this point. Add wine, stirring to deglaze any brown bits off the bottom of the pan. Cook until liquid is fully absorbed and evaporated, another 1-2 minutes.
Reduce heat to medium-low and add warm broth ½ cup at a time, stirring until absorbed. Continue adding broth in ½ cup additions for 25-30 minutes and stirring every couple of minutes until rice is cooked al-dente (it should have a slightly firm bite), the risotto is creamy and squash is tender.
Remove from heat, add parmesan, butter and sage. Serve with freshly cracked pepper.