In a large saucepan, melt the butter in the olive oil. Add the barley and cook over moderate heat, stirring, until evenly toasted, about 12 minutes. Add the onion and cook, stirring, for 2 minutes. Add the stock, bay leaves and 2 teaspoons each of salt and pepper and bring to a boil. Reduce the heat to low and simmer, stirring occasionally, until the barley is tender but still a little chewy and the stock has been absorbed, about 50 minutes. Discard the bay leaves and season the pilaf with salt and pepper. Transfer to a bowl and serve.