Heat the oven to 425°F. On a rimmed baking sheet, toss the squash with 1 tablespoon of the olive oil, 1/2 teaspoon of the salt and the pepper. Spread it out in a single layer and roast for 20 to 25 minutes, turning once, until tender and browned at the edges.

While the squash roasts, bring the broth to a bare simmer in a saucepan. Keep it warm over low heat.

In a large, wide saucepan or Dutch oven, heat 1 tablespoon of the olive oil and 1 tablespoon of the butter over medium heat. Add the onion and the remaining 1/4 teaspoon salt and cook for about 5 minutes, until soft. Stir in the garlic and chopped sage for 30 seconds.

Add the rice and stir for 2 minutes, until the edges of the grains turn translucent. Pour in the wine and stir until it is almost completely absorbed.

Add the warm broth one ladle (about 1/2 cup) at a time, stirring often and waiting until each addition is mostly absorbed before adding the next. Keep going for 18 to 22 minutes, until the rice is creamy and tender with just a little bite left in the center. You may not need all of the broth.

Mash about half of the roasted squash with a fork. Stir the mashed squash and the squash cubes into the risotto along with the remaining 1 tablespoon butter, the cheese and the nutmeg. Taste and add more salt if needed. If the risotto seems stiff, loosen it with a splash of warm broth; it should flow slowly when you spoon it onto a plate.

For the crispy sage, heat the remaining 1 tablespoon olive oil in a small skillet over medium heat. Add the whole sage leaves and fry for 30 to 60 seconds, until they darken slightly and stop sizzling. Lift them out onto a paper towel; they will crisp as they cool.

Spoon the risotto into warm shallow bowls and top with the crispy sage and extra cheese. Serve right away.