Instructions

Preheat grill or grill pan to medium high heat.

Combine the first 5 ingredients (ground beef through pepper) being careful not to overwork. Make 4 patties a bit larger in circumference than the hamburger buns and use your thumb to make a nickel-size indentation. a little more than ¼ inch deep, in the center of each patty. This prevents the burger from doming into a ball, keeping it flat and even as it cooks.  

Grill each burger for approximately 4 - 5 minutes per side, until a thermometer inserted in thickest portion reads 155°F. After removing burgers from the grill, cover loosely with foil, and let rest for 5-10 minutes. Juices are retained if the meat is allowed to rest.

Grill the tomato slices, 1 minute per side.  

Spread 3/4 teaspoon Dijon mustard over bottom half of each roll; top with 1 lettuce leaf, 1 burger, 1 tomato slice, and top half of roll.