Move ground beef and the cheese from the refrigerator to the counter for approximately 20 minutes to remove the chill while preparing the rest of the ingredients.
Using gloved hands, shape the ground beef into a ball.
Place it onto a cutting board and press down until a hamburger patty is formed.
Sprinkle 1/4 teaspoon each of kosher salt, coarse ground black pepper, and onion powder over each side of the patty.
Gently press the seasonings into the meat.
Toasting the Bun
Preheat a small skillet over medium-low heat until hot.
Spread softened butter over the cut sides of the hamburger bun.
Place the bun halves, butter-side down, in the skillet.
Toast for 2-3 minutes, or until lightly browned, then transfer to a plate.
Cooking the Meat
Preheat the cast iron skillet over medium-high heat until hot.
Cook the patty for about 3 minutes, then flip.
Cook for 1 minute, then add the sliced cheese.
Continue cooking for approximately 2-3 minutes, until the cheese is melted and the center of the burger reaches 160°F.
Cook for an additional 2-3 minutes if you prefer a more well-done burger.
Assembly Process
Blot excess moisture from the tomato slices with a paper towel, then sprinkle the slices with 1/8 teaspoon table salt.
Spread the mayonnaise on the cut side of the top bun, followed by the mustard and ketchup.
Place the salted tomato slices and iceberg lettuce over the condiments.
Place the cooked cheeseburger patty on the bottom bun.
Place the top bun over the burger and secure with a toothpick.