Bring 7 cups broth to boil in large saucepan. Cover and reduce heat to low.
Melt butter in heavy large pot over medium heat. Add onion and sauté until tender, about 5 minutes. Add squash and 1 1/2 teaspoons rosemary; sauté 4 minutes to coat with butter.
Add rice and stir 2 minutes. Add wine and simmer until evaporated, about 1 minute. Add 7 cups hot broth; bring to boil. Reduce heat and simmer uncovered until rice is just tender and risotto is creamy and slightly soupy, adding more broth by 1/4 cupfuls as needed to maintain consistency and stirring occasionally, about 18 minutes. Stir in spinach, and Parmesan cheese. Season to taste with salt and pepper.
Transfer risotto to large bowl. Sprinkle with blue cheese and remaining 1/2 teaspoon rosemary and serve.
Makes 6 servings.
Adapted from Bon Appétit, February 2005.