Heat 1 tablespoon butter and olive oil in a large dutch oven or skillet over high heat. Add squash and sprinkle with salt, pepper, sage, and nutmeg. Cook for several minutes, turning gently with a spatula, until squash has browned and softened. Remove to a plate and set aside.
Add 2 tablespoons butter to the same dutch oven or skillet over medium-low heat. Add onions and garlic and cook for 2 to 3 minutes, or until translucent. Add white wine, let reduce for 3-4 minutes. Add Arborio rice and stir, cooking for 1 minute.
Reduce heat to low. Add 1 cup of broth, stirring to combine. As soon as the liquid disappears, add in another cup of broth. Continue this process, stirring as the rice starts to become tender. Add salt, pepper to taste along the way.
Taste the rice after about 5 cups of broth, add 1 to 2 cups of broth additional if necessary. The rice should be chewy, but not hard.
When the rice is fully cooked, add in the cooked squash and turmeric and stir it in gently. Add the cream, Parmesan shavings, and hazelnuts. Stir until combined.
Garnish with more toasted hazelnuts and parmesan cheese. Enjoy!