Divide the ground beef into 4 equal loose balls, keeping them cold to maintain juiciness.
Preheat the cast-iron skillet over medium-high heat until it’s hot and begins to shimmer, with a slight smoke in the air.
Add a teaspoon of vegetable oil to the skillet and swirl to coat the surface evenly.
Place a beef ball onto the skillet and smash it flat with a sturdy spatula, pressing down firmly until it’s about ¼ inch thick and has a wide, even sear.
Sprinkle salt and freshly ground pepper generously over the patty as it sizzles, and cook for about 2-3 minutes until the edges are deep golden brown and juices bubble around the sides.
Use a spatula to flip the patty carefully, aiming for a deep brown crust on the cooked side, and place a slice of cheese on top immediately to melt.
Cook for an additional 1-2 minutes until the cheese is gooey and the patty is cooked through.
While the patties finish cooking, lightly toast the buns in the skillet or in a toaster until golden and crisp.
Assemble the burger by placing the cooked patty with melted cheese onto the toasted bun, then layer with pickles, onions, lettuce, and your preferred condiments.
Top with the other half of the bun, give it a gentle press, and serve immediately while hot and crispy.
