Add onion and sauté until tender, about 5 minutes Add squash and 1½ 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 ¼ cupfuls as needed to maintain consistency and stirring occasionally, about 18 minutes Stir in spinach, cream, and Parmesan cheese.
Transfer risotto to large bowl.
Sprinkle with blue cheese and remaining ½ teaspoon rosemary and serve.