How to Make It
In a bowl, combine the ground meats, mixing gently with your hands. Divide the meat into 4 pieces and gently shape each into a 3/4-inch-thick patty. Set the burgers on a baking sheet, cover with plastic wrap and refrigerate until firm, at least 2 hours.
Light a grill or preheat a grill pan. Generously season the burgers on both sides with salt. Grill over high heat until browned outside and medium-rare within, about 3 minutes per side. Transfer to a rack and let rest for 3 minutes, then set the burgers on the buns and serve.
Ground skirt steak can replace the ground brisket, the ground short rib or both.