Divide the beef (no seasoning yet) into 8 loose balls of about 75 g each and let them come to room temperature. Mix all the sauce ingredients and adjust to taste, this could easily become your signature sauce.
Heat the plancha or cast iron pan until screaming hot and add a small amount of oil. The hotter the surface, the better the burger.
Place a beef ball on the hot surface and immediately smash it flat using a sturdy spatula or burger press. As thin as possible - the thinner, the better. Season generously with salt and pepper and cook for about 90 seconds. Don’t touch it!
Flip the burger, immediately add the cheese, and cook for another 30–45 seconds.
Slice the buns and toast the cut sides in a little butter until golden brown. Build the burger: sauce first, then a patty, followed by onion and pickles, another patty, optional extra sauce, top bun, and you’re done.