Use cold butter and grate it. The most important part about adding butter to your burgers is making sure it’s a similar shape and temperature to the ground beef. For example, cubed and sliced butter left deep pockets in the beef as it cooked out, but I found that cold, grated butter makes for the perfect buttery flavor and texture.
Be gentle when mixing and shaping. Using cold butter and beef will make handling the beef a little bit easier, but you’ll still want to avoid over-mixing or being too rough while shaping the patties.
Salt the burgers after shaping. Instead of incorporating the salt into the burger patties, which can draw out moisture and make the patties dry, season the outside of the patties before grilling.