In a large saucepan, heat the olive oil. Add the onion, season with salt and pepper and cook over moderate heat, stirring, until softened, about 5 minutes. Add the rice and cook, stirring, for 1 minute. Add the wine and cook, stirring until the wine is absorbed. Add 1 cup of the warm stock and cook over moderate heat, stirring constantly, until nearly absorbed. Continue adding the stock 1/2 cup at a time, stirring constantly, until it is nearly absorbed between additions. The risotto is done when the rice is al dente and suspended in a thick, creamy sauce, about 20 minutes total. Season with salt and pepper.