First, preheat your griddle or skillet on high heat, then reduce to medium-low. This ensures an even cooking surface and prevents the burgers from burning.
Use a mandolin or a sharp knife to thinly slice the onion. The slices should be thin and uniform to cook evenly. A mandolin is preferred for its precision, but a knife will work if you don’t have one.
Measure out 6 oz portions of ground beef for each patty using a kitchen scale. Form the ground beef into loose balls without compacting too tightly. This helps keep the burgers juicy and ensures they cook evenly. Remember, we want the patties to be a bit loose to achieve that classic texture.
Place the beef balls onto the preheated griddle. Let them cook for about 10 seconds to form a slight crust.
Using a burger press or a sturdy spatula, smash the beef balls down into thin patties. Hold for a few seconds to maintain the shape. Season with salt and pepper.
Once the patties have started to develop a crust, place a handful of the thinly sliced onions on top of each patty. Gently press the onions into the meat.
Carefully flip the patties so the onions are now on the bottom, in direct contact with the griddle. Cook for another 2-3 minutes until the onions are soft and caramelized.
While the patties are finishing, place the hamburger buns cut-side down on the griddle next to the patties. Let them steam and absorb the burger juices for about 1-2 minutes. After steaming, toast the buns on the griddle until golden brown.
If desired, prepare a quick burger sauce by mixing mayonnaise, ketchup, a dash of Worcestershire sauce, and some relish.
Place a patty (with the caramelized onions on top) on the bottom half of each bun. Add 2 slices of bread and butter pickles on top of each patty. Spread the optional burger sauce on the top half of each bun. Close the burgers with the top buns.