With a serrated knife, cut the top off the extra bun half, leaving about a 3/4-inch-thick slice.
That will be the middle bun of your sandwich.
Place the three bun halves on a hot pan or griddle, face down, and toast them to a light brown.
Set aside, but keep the pan hot.
Divide the ground beef in half and press into two thin patties slightly larger than the bun.
Cook the patties in the hot pan over medium heat for 2 to 3 minutes on each side.
build the burger in the following stacking order from the bottom up: bottom bun, half of dressing, half of onion, half of lettuce, American cheese, beef patty, middle bun, remainder of dressing, remainder of onion, remainder of lettuce, pickle slices, beef patty, top bun.