Although the sandwich is most commonly served with a cup of jus or broth on the side of the plate, into which the sandwich is dipped as it is eaten, this is not how the sandwich was served when it was invented.
Two restaurants in Los Angeles have claimed to be the birthplace of the French dip: Cole's Pacific Electric Buffet and Philippe The Original. At both of these restaurants, the roll is dipped into the hot beef juices before the sandwich is assembled, and the sandwich is served "wet." The sandwich can also be requested to be served "double dipped" at either establishment. Philippe's own brand of spicy mustard is traditionally used by its patrons to complement the sandwich.
This controversy over who originated the sandwich has not been resolved definitively. Both restaurants were established in 1908. However, Cole's claims to have originated the sandwich shortly after the restaurant opened in 1908, and Philippe's claims that owner Philippe Mathieu invented it in 1908. Cole's was the oldest restaurant or bar in Los Angeles operating continuously since its opening at the same location, however, it is currently closed for remodeling as of March 15, 2007, ending its "operating continuously" streak.
The French dip is now served at a number of restaurant chains including fast food, diners and standard restaurants; however, other locations choose to serve the sandwich with jus on the side rather than already dipped.