Jamie Oliver just might be the most popular chef in the world. In just four frantic years, he s gone from low-ranking pasta cook at London s trendy River Cafe to a household name as the Naked Chefa title earned by his strippeddown style of cooking. His boyish looks, infectious enthusiasm, and matey appeal have won him the kind of popularity usually accorded to pop stars. More than a young icon, his dynamic TV series "Jamie s Kitchen"in which he trained...