Preheat your oven to 400°F (200°C). Toss the cubed butternut squash with 1 tablespoon olive oil, season with salt and pepper, and spread in a single layer on a baking sheet.
Roast the squash for 25-30 minutes until caramelized and tender, stirring halfway through.
While the squash roasts, place your warm broth in a saucepan over low heat.
Heat the remaining tablespoon of olive oil in a large, heavy-bottomed pan over medium heat. Add the diced onion and sauté for 4-5 minutes until translucent but not browned.
Add the minced garlic and cook for another 30 seconds until fragrant.
Add the Arborio rice to the pan and stir continuously for 2-3 minutes until the edges become translucent while the centers remain white.
Pour in the white wine and stir constantly until almost completely absorbed, about 2 minutes.
Begin adding the warm broth one ladleful (approximately ½ cup) at a time, stirring frequently until each addition is almost completely absorbed before adding the next. This process takes about 18-22 minutes total.
When the rice is nearly finished (after about 16-18 minutes of adding broth), gently fold in the roasted butternut squash, reserving a few pieces for garnish if desired.
Remove from heat and stir in the butter, Parmesan cheese, chopped sage, and nutmeg.
Cover and let rest for 2 minutes to allow the flavors to meld.
Season with salt and freshly ground black pepper to taste.
Serve in shallow bowls, garnished with additional roasted squash pieces, fried sage leaves, and toasted pumpkin seeds if desired.