Heat olive oil in a large pot over medium heat.
Add chopped onion and cook until translucent, about 5 minutes.
Add minced garlic and cook for another minute.
Stir in Arborio rice and cook for 2 minutes, until rice is lightly toasted.
Pour in white wine (if using) and cook until mostly absorbed.
Begin adding warm vegetable broth, one ladle at a time, stirring constantly and allowing each addition to be absorbed before adding the next.
After 15 minutes, add butternut squash cubes to the pot. Continue adding broth and stirring.
After about 20 minutes, when the rice is tender and the squash is cooked through, stir in grated Parmesan cheese.
Season with salt and freshly ground black pepper to taste.
If desired, stir in a tablespoon of butter for extra creaminess.
Serve hot, garnished with additional Parmesan cheese if desired.