From America's Test Kitchen
We know that many backyard cooks grill their burgers to medium-well and beyond, but we aren’t willing to accept the usual outcome of tough, desiccated hockey pucks with no beefy flavor. We wanted to work with supermarket ground beef to produce a tender and moist-as-can-be burger, with perfect grill marks and all, even when well-done.
Taste tests proved that well-done burgers made with 80 percent lean chuck were noticeably moister than burgers made from leaner beef, but they still weren’t juicy enough. Because we couldn’t force the meat to retain moisture, we opted to pack the patties with a panade, a paste made from bread and milk that’s often used to keep meat loaf and meatballs moist. To punch up the flavor, we also added minced garlic and tangy steak sauce. To keep our burgers from puffing up the way most burgers do, we made use of a previous test kitchen discovery: If you make a slight depression in the center of the patty, it will puff slightly as it cooks and level out to form a flat top.
Adding a panade (a paste of bread and milk paste) to the ground beef creates burgers that are juicy and tender even when well-done. For a burger that cooks up flat, press the center of each patty down with your fingertips before grilling. Serve the burgers on your favorite buns or rolls. For cheeseburgers, follow the optional instructions below.