Preheat oven to 425F. Cut the squash in half length-wise and place face down on a foil-lined cookie sheet. Roast for 60 minutes, or until squash is soft.
Scoop the inside of the squash out and puree with an immersion blender, food processor or regular blender until smooth and creamy. (you want about 2 cups total.) Set aside
For the Risotto:
Melt the butter in a large saucepan over medium-high heat. Add the onion and cook for 5-8 minutes, or until the onions are soft and translucent. Add the rice, and cook, stirring frequently for 5 minutes more, or until the onions begin to brown on the edges.
Pour in the wine and stir constantly, until it has evaporated. Add in 1/3 of the broth and reduce heat to medium. Cook and stir until all the broth has been absorbed by the rice. Add half of the remaining broth, and continue stirring until it has been absorbed. Finally, pour in the remaining broth, and continue stirring until risotto is thick and all the liquid has been worked in.
Stir in the squash, and the parmesan cheese until smooth and creamy. Add salt and pepper to taste.