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 - In a large, heavy saucepan, heat remaining 1 tablespoon olive oil and 1 tablespoon butter over medium heat. Add onion and cook until translucent, about 4 minutes. Add garlic and cook for 1 minute.
03 - Stir in Arborio rice and cook, stirring, until edges are translucent, about 2 minutes.
04 - Pour in white wine and stir until mostly absorbed.
05 - Begin adding warm broth, 0.5 cup at a time, stirring frequently. Wait until each addition is nearly absorbed before adding the next.
06 - After 15 minutes, fold in roasted squash and chopped sage. Continue adding broth and stirring until rice is creamy and al dente, about 20–25 minutes total.
07 - Remove from heat. Stir in remaining 2 tablespoons butter and grated Parmesan until melted and creamy. Season generously with salt and pepper.
08 - Serve immediately, garnished with extra Parmesan and a few fresh sage leaves if desired.