Grilled Mustard Dill burgers

Be very gentle when forming these burger patties. Even more careful when grilling them. I promise the extra care is worth it.
From Epicurious again
3 tablespoons sour cream
3 tablespoons Dijon mustard
1 1/2 tablespoons chopped fresh dill
10 ounces lean ground beef
2 hamburger buns, split
2 tomato slices
2 Bibb lettuce leaves

Mix first 3 ingredients in medium bowl.
Add half the sauce to the meat in medium bowl and mix gently.
Divide meat mixture into 2 equal portions.
Flatten each to 1/2-inch-thick patty; sprinkle with salt and pepper.
Grill cut side of buns until toasted, about 1 minute.
Grill patties to desired doneness, about 4 minutes per side for medium.
Spread bottom half of buns with reserved sauce.
Top each with burger, tomato slice, lettuce and bun top.