the idea is to get a lovely maillard reaction, that is get a nice
browned sear, to enhance flavor, and lock the juices inside. i'll never
make burgers another way unless i'm headed for a weekend of drunken
camping and grab a box of frozen patties at a store.
i take 1 lb ground sirlon and season it. then 1/4 the sirloin into 1/4
pound portions and roll them into meatballs. preheat a griddle or pan,
whatever works, set the meatballs one at a time on the nice hot griddle
and flatten them until they're about 3/8 inch thick with a bacon press
as mentioned above, or a small saucepan with wax or parchment paper
between the man and the meat. don't lift or slide them around until they
are ready to flip, and then only flip them exactly once, and give them
another press onto the griddle. it takes a bit of practice to know when
to flip them, you can tell by the juices coming to the top of them.
for better info on when to flip them (visuals are worth a thousand
words), are plenty of videos about making smashburgers on youtube.