01 - Preheat oven to 400°F. Toss diced squash with 1 tablespoon olive oil, salt, and pepper. Spread on a baking sheet and roast for 20–25 minutes until tender and lightly browned. Set aside.
02 - Heat remaining 1 tablespoon olive oil and 1 tablespoon butter in a large saucepan over medium heat. Add chopped onion and cook until translucent, about 4 minutes. Add minced garlic and cook for 1 minute more.
03 - Add Arborio rice and cook, stirring, until the edges become translucent, approximately 2 minutes.
04 - Pour in white wine and stir continuously until mostly absorbed.
05 - Add warm vegetable broth in increments of ½ cup, stirring frequently and allowing each addition to be mostly absorbed before adding the next.
06 - After about 15 minutes of cooking, fold in the roasted squash and chopped sage. Continue adding broth and stirring until the rice is creamy and cooked al dente, totaling 20 to 25 minutes.
07 - Remove from heat. Stir in the remaining 2 tablespoons butter and grated Parmesan cheese until melted and creamy. Adjust seasoning with salt and freshly ground black pepper.
08 - Serve warm, garnished with extra Parmesan and fresh sage leaves if desired.