Wash and dry produce.

Quarter lemon.

In a small bowl, combine ketchup, half the mayonnaise, half the sour cream, half the mustard, ¼ tsp sugar, ¼ tsp Fry Seasoning (you’ll use the rest in the next step), juice from one lemon wedge, ½ tsp salt, and pepper. (For 4 servings, use ½ tsp sugar, ½ tsp Fry Seasoning, juice from two lemon wedges, and 1 tsp salt.)

In a medium bowl, gently combine beef*, remaining mustard, remaining Fry Seasoning, a big pinch of salt, and pepper. Form beef into two equal-size balls (four balls for 4 servings).

Heat a drizzle of oil in a large pan over medium-high heat. Once pan is hot, add beef; firmly flatten each ball with a lightly oiled spatula to create patties, each slightly wider than a burger bun. Cook until browned and cooked through, 3-5 minutes per side. (Don’t worry if the patties aren’t perfectly round—those irregular edges will turn crispy.) 

Meanwhile, in a second medium bowl, combine coleslaw mix, remaining mayonnaise, remaining sour cream, ¼ tsp sugar (½ tsp for 4 servings), juice from two lemon wedges (four lemon wedges for 4), a pinch of salt, and pepper.

Halve buns; toast until golden.

Spread a thin layer of tangy mayo on bottom buns. Fill buns with patties, crispy fried onions, and as much remaining tangy mayo as you like.

Divide burgers and slaw between plates. (You can also top burgers with a bit of slaw for an authentic deli special.) Serve.