Pour the stock into a 2-quart saucepan and keep it hot over low heat. Heat the olive oil in a braising pan over medium heat. Stir in the onion and cook stirring occasionally, until softened, about 4 minutes. Stir in the rice and continue stirring until the grains are coated with oil and the edges become translucent - 1 to 2 minutes. Pour in the wine and let it boil, stirring the rice, until evaporated. Season the rice lightly with salt and ladle enough of the hot stock into the pan to barely cover the rice. Bring to a boil, then lower the heat so the stock is at a simmer. Cook, stirring constantly until all the stock has been absorbed. Continue cooking, pouring in the remaining hot stock in small batches and cook until each batch of stock has been absorbed. Stir constantly until the rice mixture is creamy, 16 to 20 minutes. Add pumpkin, ginger, nutmeg and basil and simmer until heated through. Remove the pan from the heat and stir in the butter until completely melted.