Heat the olive oil in a saucepan over medium heat. Add the onion and garlic, and cook until softened.
Add the Arborio rice and cook, stirring constantly, for 2-3 minutes until the rice is lightly toasted.
Stir in the pumpkin puree and cook for another minute.
Begin adding the warm vegetable broth, one ladle at a time, stirring frequently. Wait until the liquid is mostly absorbed before adding more broth. Continue this process until the rice is creamy and cooked through, about 20-25 minutes.
Stir in the Parmesan cheese and fresh sage. Season with salt and pepper to taste.
Serve immediately, garnished with additional Parmesan cheese and sage if desired.