I’ve pretty much settled on plain old yellow mustard for these burgers. That’s what you got when you ordered at a diner and that was what was in the plastic take-out packets, and that’s the flavor I remember and still want. I buy jars of whole dill pickles and slice them with a small mandoline so that they will be right. Raw onion, sliced thin. I want the flavor but I don’t want them to crunch like taking a bite from an apple.