For the sauce:
1 cup sour cream or Greek yogurt
About ¼ to ⅓ cup ketchup
3 tablespoons dill pickle relish
2 tablespoons Worcestershire
Salt and pepper
For the burgers:
2 ¼ to 3 pounds ground beef sirloin (80% lean), or about 1 ½ pounds plant-based meat (Rach likes Impossible)
2 slices yellow American cheese, per patty
6 soft sesame seed buns (Rach likes Big Marty's)
1 small Vidalia or white onion, finely chopped
Dill pickle chips
½ head iceberg lettuce, cored and chopped
Combine sauce ingredients in small bowl.
For beef sirloin, form 6- to 8-ounce patties thinner at center than edges for even cooking.
For plant-based meat, form thin patties, 4 to 5 ounces each, and season with salt and pepper.
Grill or cook patties in a preheated cast iron skillet over medium-high heat, 7 to 8 minutes, turning occasionally, and melt cheese on patties last 1 to 2 minutes.
To build Big Smack: bun bottom, onions, chopped iceberg lettuce, dill pickle slices to cover surface, patty with American cheese, special sauce, and bun top.