A French dip sandwich (or beef dip) is thinly sliced roast beef piled on a French roll or baguette and served with a side of au jus for dipping. Its exact origin is disputed: it's most often credited to Philippe's or Cole's, two competing early-20th-century Los Angeles restaurants, each with its own account of the first dip. The au jus is the thin, unthickened pan drippings from roasting the beef, simmered with stock and aromatics; it is not a thickened gravy, and the distinction matters here, since a heavier gravy would oversaturate the bread. Variations swap in turkey, pastrami, or pork, and may add melted provolone or Swiss, grilled onions, or peppers.