Roast the pumpkin by tossing cubes with 1 tablespoon olive oil, salt, and pepper. Spread on a baking sheet and roast at 400°F for 20-25 minutes until tender and edges are caramelized. Set aside ¼ of the roasted pumpkin for garnish, and mash the remainder with a fork.
Heat stock in a saucepan until it’s steaming but not boiling. Keep it warm throughout the cooking process – this is crucial for proper risotto texture.
Sauté the aromatics by heating the remaining olive oil and 1 tablespoon butter in a heavy-bottomed pot over medium heat. Add onions and cook for 3-4 minutes until translucent, then add garlic and cook for 30 seconds until fragrant.
Toast the rice by adding it to the pot and stirring constantly for 2-3 minutes until the edges become translucent but the center remains white. This crucial step helps the rice release its starches properly.
Deglaze the pot with white wine, stirring constantly until the liquid is almost completely absorbed and the alcohol smell has dissipated.
Begin adding stock one ladleful at a time (about ½ cup), stirring frequently until almost completely absorbed before adding the next. This gradual process takes patience but creates the perfect texture.
Incorporate the mashed pumpkin after about 15 minutes of adding stock, along with the sage, thyme, and nutmeg. Continue adding stock and stirring until rice is al dente – tender but with slight resistance when bitten.
Finish the risotto by removing from heat and stirring in the remaining tablespoon of butter and the Parmesan cheese. Cover and let rest for 2 minutes to achieve ultimate creaminess.
Serve immediately with reserved pumpkin cubes on top, extra Parmesan, freshly ground black pepper, and toasted pumpkin seeds if desired.