For the Sauce: Whisk together mayo, ketchup, relish, and smoked paprika until well-combined. Cover and refrigerate until ready to use for burgers.

Burgers: Prepare the patties: Line a plate with wax paper. Divide beef into four equal (4oz/113g) pieces. Use your hands to loosely form each into a round ball. Do not overwork the meat, just gently form it into a ball.

Season and chill: Place meatballs on a wax paper lined plate and sprinkle the tops with salt and pepper. Keep cold in fridge or freezer while you preheat your pan.

Prepare the pan: Drizzle a teaspoon of oil over a cast iron pan and use a paper towel to smear it evenly over the surface. Turn heat to medium-high and heat until pan is smoking.

Smash the burgers: Add a ball of meat to the pan. Immediately use your burger press or large spatula to firmly press straight down on the burger and smash it flat (if using a spatula, grip a mallet and use that to help you press into the burger, see photo in post for visual if needed). If meat sticks to the press, you may place a square of parchment paper over it before flattening.

Cook for approximately 1 minute, until a crust has formed on the burger (avoid the temptation to re-squish the burger or flip it early!). Sprinkle with more salt and pepper while it cooks.

Flip. Use spatula to scrape up the burger (you want to be sure to scrape up all the caramelized crust and not leave anything behind), flip, and add a slice of cheese if desired. Cook through (approximately 45 seconds longer). Transfer burgers to a clean plate and cover with foil while you toast the buns.

Toast the buns: Immediately add butter to the hot pan. Once melted, turn off pan and place burger buns cut-side down on the skillet and cook briefly, until warm and toasted on the bottom.

Assemble & enjoy: Spread burger sauce onto toasted buns, top with burgers and any additional desired toppings and enjoy immediately.