Mitchell started cooking in New York where he embarked on a two year comprehensive apprenticeship at the famed Four Seasons Restaurant where he met his mentor, Chef Seppi Renggli. Within three months he received the unprecedented honor of being promoted to grill cook and put on salary. He cooked side-by-side Renggli in the Grill Room. He then joined the kitchen at Le Cirque in NYC and Gitane, in NJ with brother Steven, before returning to Four Seasons. In 1989, he contacted Wolfgang Puck who was opening Postrio in San Francisco and became one of the opening cooks. He left Postrio after a year to further explore the culinary treasures of Asia and Europe. Upon returning to the U.S. he worked for Wolfgang Puck at his Mediterranean restaurant, Granita in Malibu and then at the Italian restaurant Coco Pazza in NY. In 1994, Mitchell returned to San Francisco when Wolfgang Puck contacted him and his brother and asked them to be the Executive Chefs of Postrio Restaurant. Michael Bauer of The San Francisco Chronicle called the trio of Wolfgang Puck, Mitchell Rosenthal and Steven Rosenthal “all shockingly good cooks.” Mitchell and Steven lifted Postrio to four stars.