Anybody solving my favorite mystery in American history will ease my frustration at my own failure to do so. Twenty years ago for a book in process I set myself to find out who invented the hamburger—not its grandfather, the German-born “Hamburger steak,” a broiled mound of chopped beef eaten with knife and fork, but the browned patty tucked into a plump white roll that became the worldwide symbol of American gastronomy. I did draw some blood: Around 1900 Louis’ Lunch in New Haven was serving a broiled beef-patty sandwich, but that was on sliced bread, not the roll, as essential to the classic hamburger as potatoes are to clam chowder. I managed to trace a rapid infiltration of a “hamburger” item into lunch wagons and carnival lots well before World War I but turned up no definite point where the roll took over. People kept telling me roll-hamburgers first appeared at the St. Louis World’s Fair of 1904. But local archives had no trace of such a thing, nor did Thomas Hart Benton when I asked him about it: “No, sir, I had a growing boy’s appetite, and I was all over that fair every day—no hamburgers.”

Possible solution: A late-at-night run on bread-hamburgers in some one-arm lunch around 1905 exhausted the bread supply, the cook substituted the rolls then used for ham sandwiches—very filling but very little ham—and the customers liked the innovation because it held together better in the hand.

But where, oh where, was that all-night lunchroom and who was that cook?