In a small bowl combine mayonnaise, ketchup, yellow mustard, sweet pickle relish, finely grated onion, apple cider vinegar, Worcestershire sauce, smoked paprika, salt and black pepper. Mix until smooth and well incorporated. Taste and adjust seasoning; refrigerate at least 15 minutes to let flavors meld. Makes about 4 tablespoons.

Burger

Form the 10 oz ground beef into a single loose patty about 3/4 inch thick, slightly wider than the bun. Do not overwork the meat; handle gently and create a shallow indentation in the center with your thumb to help it cook evenly.

Season both sides of the patty with kosher salt and freshly ground black pepper just before cooking.

Heat a cast-iron skillet or grill over medium-high heat until very hot. Add 1 tablespoon neutral oil and swirl to coat (if using a grill, oil the grates lightly).

Place the patty on the hot surface and cook undisturbed for 3 to 4 minutes to develop a crust. Flip once and cook another 3 to 4 minutes for medium (adjust time 1–2 minutes more for medium-well).

About 1 minute before the patty is done, place the Swiss cheese slice on top and cover the pan or close the grill lid to melt the cheese.

Remove the patty from the heat and let rest on a plate for 2 minutes while you assemble the bun.

Bun & Assembly

Butter the cut sides of the burger bun with 1/2 tablespoon softened butter. Toast in the same skillet or on the grill cut-side down over medium heat until golden and fragrant, about 1 minute.

Spread a generous layer (about 1 to 1 1/2 tablespoons) of the prepared special sauce on the bottom bun.

Place the Swiss-topped burger patty on the sauced bottom bun.

Top the patty with lettuce leaf, tomato slices, pickle slices and onion rings in that order (or rearrange to preference). If desired, add an extra dollop of sauce on the top bun.

Close the burger with the top bun, press gently to set, slice in half if serving, and serve immediately.