In medium saucepan over medium-high heat, heat chicken stock until simmering, then reduce heat to low and let simmer.

Heat oil in large, deep-sided skillet over medium-high heat. Add onion and butternut squash and cook until beginning to soften, 8 to 10 minutes. Season with salt and pepper.

Add rice and let cook 1 minute, stirring constantly. Add white wine and simmer, stirring frequently, until nearly absorbed, 2 to 3 minutes.

Reduce heat to medium and add 1/2 cup stock. Let simmer until absorbed, stirring frequently. Continue adding stock and simmering until all stock has been used, about 15 minutes.

Stir in rosemary, butter, and Parmesan. Serve risotto topped with additional grated Parmesan.