In a large saucepan over medium heat, add 1 teaspoon olive oil and diced onions. Cook for about 20 minutes, until onions are translucent.
Add Arborio rice and cook until golden brown, about 3 minutes.
Pour white wine over rice and add pinch of saffron. Cook over medium heat, stirring constantly, until wine is absorbed.
While risotto is cooking, place a large sauté pan over high heat, add 3 tablespoons butter and allow to foam. When ready, add diced squash and cook until caramelized and tender. Remove pan from heat and add walnuts and sage.
Add 2 cups chicken stock to rice, adding more as it is absorbed. Stir frequently. Cook in this manner for about 30 minutes. Taste for doneness and season with salt and pepper.
Once the rice is cooked remove from heat. Add 2 cups warm pumpkin purée, 2 tablespoons butter, 2 tablespoons mascarpone, and 2 tablespoons Parmesan. Stir to combine, taste and adjust final seasoning.
Serve risotto in shallow bowls and top with sautéed squash, walnuts and sage.
In a medium saucepan over medium heat, add walnuts and brown sugar.
Cook for about 5 minutes, stirring constantly, until sugar is melted and nuts are completely coated.
Pour nuts onto a prepared baking sheet, spread into a single layer, sprinkle with salt and allow to cool.
Once ready, chop nuts to desired size.