01 - Melt butter in a large skillet over medium heat. Add sliced onions, sugar, and salt. Cook for 20–25 minutes, stirring occasionally, until onions turn deep golden brown. Add a splash of water if the pan gets too dry. Remove from heat and set aside.
02 - Combine ground beef, kosher salt, black pepper, and Worcestershire sauce in a large bowl. Mix gently to avoid overworking the meat. Divide into 4 equal portions and shape into patties. Press a small indentation into the center of each patty to prevent puffing during cooking.
03 - Heat grill, grill pan, or skillet over medium-high heat. Place patties on the cooking surface and cook for 3–4 minutes per side for medium doneness. During the final minute, add cheddar cheese slices and cover to melt.
04 - Place burger buns cut side down on the grill or in a dry skillet. Toast for 1–2 minutes until golden and lightly crisp.
05 - Layer lettuce and tomato slices on the bottom bun. Add the cheese-topped patty, followed by caramelized onions and pickles. Spread ketchup, mustard, or mayonnaise as desired. Crown with the top bun and serve immediately.