Heat 2 tablespoons of the oil in a large saucepan. Add the onion; cook over low heat, stirring, until softened. Stir in the rice until evenly coated. Add the wine; simmer over moderate heat, stirring, until fully absorbed. Add 1 cup of the hot stock and cook, stirring constantly, until almost absorbed. Add 5 more cups of stock, 1 cup at a time, stirring until absorbed between additions. The risotto is done when it is creamy and the rice is al dente, about 20 minutes total. Cover and keep warm.