To prepare the onion rings, heat about 2" of oil in a saucepan to 350F. Meanwhile, mix together the all purpose flour, garlic powder, salt, and buttermilk in a bowl until smooth. Dip your onions into the mixture to coat. Let the excess drip off and cover with panko or breadcrumbs. Fry the onions rings off in the hot oil until golden brown. Drain on a towel and season with salt. Keep the onion rings warm in a low oven while you prepare the burger.
Heat a cast iron pan over high heat. Divide the beef into quarters and season with salt and pepper. Shape the beef into patties. Once the pan is screaming hot, add the oil and the patties. Let it cook for one minute on one side and flip. Cook for another 3-5 minutes depending on how you like your burgers.
Arrange your burgers with the ketchup, burger, and your toppings. It's a hefty burger so a knife might help with the presentation. Enjoy!