Preheat the oven to 400°F. Toss the cubed butternut squash with 2 tablespoons olive oil, salt, and pepper on a baking sheet. Roast for 25 minutes until the edges turn golden and the pieces soften.

Warm the vegetable broth in a pot over low heat and keep it simmering gently.

Heat the remaining tablespoon of olive oil in a large skillet over medium heat. Add the diced onion and cook until it softens, about 5 minutes. Stir in the minced garlic and cook for 1 minute more.

Add the arborio rice to the skillet and stir for 2 minutes until the grains look lightly toasted.

Ladle in the warm broth one cup at a time, stirring often. Wait until each addition absorbs before adding the next. Continue until the rice turns creamy, about 18 minutes total.

Stir the chopped sage into the risotto during the last 5 minutes of cooking. Fold in the roasted squash, butter, and Parmesan cheese until everything combines evenly.

Taste and adjust salt and pepper if needed. Spoon into bowls and top with the reserved whole sage leaves.