- 2 cups mayonnaise
- 1/2 cup pepperoncini, minced
- 4 teaspoons ketchup
- 1/4 cup pickles, minced
- 1/4 cup capers, minced
- 1/2 teaspoon fresh lemon juice
- 1/4 red onion, minced
- 1/4 teaspoon kosher salt
- 1/4 teaspoon freshly ground black pepper, to taste
- 2 tablespoons vegetable oil, plus more for pan
- 2 large yellow onions, finely chopped
- Kosher salt, to taste
- 4 hamburger buns, split
- 1/4 cup dill pickles, sliced
- 3/4 cup shredded iceberg lettuce
- 4 thin slices tomato
- Freshly ground black pepper, to taste
- 2 pounds ground chuck beef (preferably 80 percent lean)
- 8 slices American cheese
- 2 large russet potatoes (about 1 1/2 lbs)
- 1/2 cup chopped fresh parsley
- 1/4 cup chopped fresh rosemary
- Truffle salt, to taste
- Fresh ground black pepper, to taste
For the thousand island dressing, combine all ingredients in a large bowl. Fold until evenly mixed.
For the burger, in a large skillet, add vegetable oil over medium heat. Add onions and 3/4 teaspoon salt, cover, and cook, stirring occasionally, until golden and soft, about 20 minutes. Uncover, increase the heat to medium-high, and continue to cook, stirring often, until caramelized, about 8 minutes. Add 1/4 cup water to skillet, scraping browned bits from bottom of pan. Simmer and stir until the water evaporates, about 2 minutes. Transfer to a bowl and set aside.
Heat a griddle or skillet over medium heat; lightly brush with vegetable oil. Toast buns on the griddle, split-side down. Spread about 1½ tablespoons dressing onto each toasted bun bottom. Top with a few pickles, lettuce, two tomato slices (make sure to season with salt and pepper), another dollop of sauce, then set aside.
Keeping the griddle hot, form ground beef into 8 patties, and season both sides with salt and pepper. Place on the griddle and cook 3 minutes, then flip and top each with 1 slice cheese. Continue cooking about 2 minutes more for medium-rare to medium doneness. Top 4 of the patties with caramelized onions, then arrange the remaining patties on top, cheese-side up. Assemble the burgers with the double-patties.
For the french fries, cut potatoes into shoestrings or matchsticks, preferably using a mandolin at the thinnest julienne setting. Rinse cut potatoes to remove excess starch and transfer to a paper towel–lined baking sheet; pat dry as much as possible. In a heavy-bottomed pot, heat 2 to 3 inches oil to 350˚F. Working in batches, fry shoestrings until potatoes are crisp and golden-brown, 2 to 3 minutes per batch. Transfer immediately to a large mixing bowl and toss with some of the chopped herbs, truffle salt, and pepper. Transfer to a paper towel-lined baking sheet.