Getting some crispiness in Burgers' crust
Crunchy (I suspect crusty is probably a better term) burgers are often made by what Kenji Alt of Serious Eats like to call the smash method, as described in The Burger Lab:  Smashed Burgers vs Smashing Burgers.

The basic technique is to form the beef into what he calls a "puck", and then cook them on a ripping hot skillet or cast iron pan, smashing them down into patties onto the hot pan.  This promotes the browning reactions and crisping on the first side of the burger.

The burgers mostly cook on that first side where the crust development will happen; the cooking on the second side is much more brief.