In a medium bowl, mix all the ingredients together until well combined. Form the beef into patties about 1/2-inch thick and about 1/4-inch larger in diameter than the buns you’ll be using. Refrigerate the patties until ready to grill.
Cook the burgers on a preheated grill over medium-high heat until the burgers are cooked to your liking (I like mine with the barest hint of pink in the center and usually grill for about 6 minutes per side).
The last two minutes of grilling, butter the inside of the bun and slap it on the grill to toast while the burgers finish cooking.
Rosemary Burger Variation: add 3-4 sprigs fresh rosemary (slide the leaves off the stalk, discard the stalk and coarsely chop the rosemary) to the ingredients and mix to combine with the beef.