Preheat oven to 375 °F.
Bake bacon on a slotted pan in the center of the oven until crispy. Cut into 2-inch jumbo bacon bits.
Combine sour cream, ketchup, relish, Worcestershire and hot sauce. Season with salt and pepper to taste.
Trim tops of 2 buns and cut them through horizontally—these pieces will separate the double-decker burgers. Split the remaining rolls and toast all the bread lightly.
Season meat with salt and pepper, and grate 3 tablespoons of onion over the meat. Form 8 thin, wide patties. Finely chop the remainder of the onion and rinse with water; reserve.
Heat a cast-iron skillet over medium-high heat with half a tablespoon of oil, a half turn of the pan. Cook 4 patties 5-6 minutes turning once; melt cheese over each patty. Repeat with remaining patties.
Assemble burgers: bun bottom, lettuce, pickles, cheeseburger, bacon bits, chopped onions sauce, middle bun layer, lettuce, pickles, cheeseburger, bacon bits, onions, sauce and bun tops.