At BK in the 1990s we “did it” like so: burgers and buns went into a “broiler/steamer” machine which did the flame broiling on top and toasted the buns on the bottom, we would assemble burgers (regular size) and whoppers (XL) and put them in the steam tray, people at the whopper board and burger board would take them out of the steam tray and put the condiments on and put them in boxes in the heat chute.

Burgers could sit in either the heat chute or the steam tray for 10 minutes and we were supposed to throw them out if they went over that limit. Under normal conditions we didn’t throw a lot of them out but we would go to a purely on demand model on Sunday afternoons when we could sometimes go 20 minutes between customers.