(FORTUNE Magazine) – Robert Sherman has moved from the Rock to the frank. The former head of retail operations for Prudential-Bache Securities is now the top dog at Nathan's Famous, the 73-year-old restaurant chain known for its frankfurters. Sherman, who was Pru-Bache's chief broker for seven years, left the investment firm last year after a disagreement with other officers over the firm's direction. ''I had been working for them for 28 years,'' says Sherman, 51. ''I needed a change.'' He also happened to be friends with Stuart Benson, chairman of the investor group that bought a majority interest in Nathan's earlier this year. So Sherman went from picking winners to cooking wieners. His opening gambit will be to continue expanding the 36-store chain beyond its New York base; he plans to open 21 units by year-end, including two on the Florida Turnpike and one in Chicago. Says he: ''The Nathan's name has been terribly underutilized. This is a marvelous opportunity to go nationwide.'' That's fine, but based on an unscientific taste test by FORTUNE at the Nathan's outlet in Times Square, Sherman faces another task -- not unlike the one the Japanese faced with the MADE IN JAPAN label, circa 1960.