A hamburger might look perfectly flat when you form the ground beef into a patty. But inevitably the burger puffs up in the center as the meat contracts while cooking. This may force a balancing act as you assemble the toppings on your burger, or lead you to overcook the meat in an effort to ensure that it's done in the thick middle. The solution lies in the steps you take before the meat meets the heat.
Form the burgers into flat patties about 1 inch wider than your hamburger buns, using your hands to shape the ground beef. Form the patties quickly, handling the meat as little as possible to prevent the meat from becoming tough.
Lay the patties on a plate or flat work surface. Press down on the center of each burger patty, using three fingers to make an indentation at least halfway through the burger thickness.
Cook the burgers on a hot grill or skillet, or under a broiler until a thermometer inserted in the center reads 160 degrees Fahrenheit. The burgers will shrink as the cook; the extra 1 inch of width ensures that the burger is roughly the same size as the bun when done. Instead of the center puffing up as the burgers shrink, the indentation will rise to the level of the meat around the edges of the patty.