Begin by roasting the sweet potatoes. Preheat your oven to 400°F (200°C). Toss the cubed sweet potatoes with a tablespoon of olive oil, salt, and pepper. Spread them on a baking sheet and roast for 25 minutes, or until tender and slightly caramelized.

In a large, heavy-bottomed saucepan, heat the remaining olive oil and butter over medium heat. Add the chopped onion and cook until translucent, about 3 minutes.

Add the minced garlic and half of the chopped sage, cooking for another minute until fragrant.

Stir in the Arborio rice, ensuring each grain is coated with the oil and butter. Cook for 2 minutes until the edges of the rice become slightly translucent.

Pour in the white wine and let it simmer until it's almost entirely absorbed by the rice.

Begin adding the warm stock, one ladle at a time, stirring constantly. Wait until each addition is almost fully absorbed before adding the next. This process can take about 18-20 minutes.

Once the rice is al dente and the risotto has a creamy consistency, fold in the roasted sweet potatoes, the rest of the sage, and the Parmesan cheese. Season with nutmeg, salt, and pepper to taste.

Remove from heat and let the risotto sit for a few minutes. This allows the flavors to meld together and the risotto to reach the perfect consistency. Serve hot, garnished with additional Parmesan cheese if desired.