Potato bun with some of the middle of the bun taken out. Too much bread can ruin a good burger. Why are you eating it, anyway?
Sautéed mushrooms and onions. Any cold ingredient once again takes away. Does lettuce really add flavor?
Bread and butter pickles, room temperature.
Smoked, reverse seared burger topped with your favorite cheese, but more than one slice. Mine is Muenster.
No burger should ever be well done. Medium at most. Use quality meat.
Pull all those hot ingredients off the grill/stove and pile it on the burger. Wrap in in aluminum foil for a minute or two so the heat steams the bun and the cheese melts all over the burger.
No need for mayo, ketchup, mustard, blah blah when the above ingredients are prepared properly. Juiciest, most flavorful burger ever. Come to the table with a roll of paper towels.