For the burger: Find a bowl or pan that is just bigger than your bread and place on a piece of parchment paper. Trace around the bowl with a pen and flip the paper over. Use the paper as a guide to shape the sirloin into a patty. Sprinkle both sides of the patty with 1 teaspoon salt.
Place a cast-iron pan or griddle over medium-high heat. Once hot, add the oil and heat until shimmering.
Add the patty to the pan and press down firmly with a spatula. Cook until the edges are crispy and deeply golden brown, 3 to 4 minutes per side. Fan the cheese over the burger and place a metal bowl or baking sheet inverted over the patty. Cook until the cheese melts and gets crispy on the edges touching the pan, about 2 minutes more.
For the special sauce: Whisk together the ketchup, mayonnaise, mustard and black pepper in a small mixing bowl.
Spread the special sauce on the cut sides of the boule. Place the burger on the bottom half of the boule. Top with the lettuce, tomatoes, pickles and a sprinkle of salt. Slice into quarters or sixths and serve.