Preheat your griddle or a large skillet on medium-high, until the cooking surface reaches about 400-425℉.

Separate the ground beef into 4 equally-sized portions, and roll into balls. Each ground beef ball should be about 4 oz in weight.

Place the ground beef balls on the preheated flat top grill or in the cast iron skillet. Top each beef ball with a large handful of sliced onions. Sprinkle salt and black pepper on each pile.

Use a stiff spatula or a burger press to smash the ground beef balls down on the cooking surface, until about 1/4 – 1/3″ thick. Allow the onion burgers to cook untouched until the outside edges of the sliced onions are lightly browned, about 3 minutes.

Flip the onion burgers to the second side, so that the sliced onions are now in contact with the cooking surface. Immediately after flipping, top each burger patty with a slice of American cheese (if using).

Stack the top and bottom bun, cut side down, on top of each patty as they cook. This allows the buns to steam in the burger fat and moisture from the onions.

Continue to cook the fried onion burgers until cooked through, about another 2-3 minutes.

Build your Oklahoma Onion Burger with one or two patties. Top with yellow mustard and pickle or your favorite burger toppings.