Preheat the oven (with the oven rack in the middle) to 400°. Shape the beef into 4 patties about 3/4" thick. Sprinkle both sides with pepper and the remaining 3/4 tea­spoon salt. Heat a large skillet, preferably cast-iron, over medium heat. Add the patties and cook for 5 to 6 minutes, until the undersides have a nice dark brown crust. Flip the patties and cook for 5 to 6 minutes more for medium doneness. Mix blue cheese and blue cheese dressing together. Transfer the burgers to a rimmed sheet pan. Dividing evenly, spread the blue cheese mixture over each burger. Bake 2 to 3 minutes. Warm your buns at the same time. Build your burgers with the buns, patties and lettuce.