01 - Preheat the oven to 400°F. Toss the diced winter squash with 1 tablespoon olive oil, salt, and black pepper. Spread evenly on a baking sheet and roast for 20 to 25 minutes until tender and lightly caramelized. Remove and set aside.
02 - Heat remaining 1 tablespoon olive oil and 1 tablespoon butter in a large heavy saucepan over medium heat. Add the chopped onion and cook until translucent, about 4 minutes. Stir in the minced garlic and cook for an additional minute.
03 - Add Arborio rice to the saucepan and cook, stirring constantly, until the edges become translucent, approximately 2 minutes.
04 - Pour in the dry white wine and stir until it is mostly absorbed by the rice.
05 - Begin adding the warm vegetable broth, half a cup at a time, stirring frequently. Allow each addition to be nearly absorbed before adding the next.
06 - After approximately 15 minutes of cooking, fold in the roasted squash and chopped fresh sage. Continue adding broth gradually and stirring until rice reaches a creamy texture and is al dente, about 20 to 25 minutes in total.
07 - Remove the pan from heat. Stir in the remaining 2 tablespoons butter and freshly grated Parmesan cheese until melted and creamy. Adjust seasoning with salt and freshly ground black pepper to taste.
08 - Serve immediately, garnished with extra Parmesan cheese and fresh sage leaves if desired.