SMASH BURGERS WITH GRIDDLED ONIONS AND SPICY SPECIAL SAUCE

Steps:

• Whisk the mayonnaise, pickled jalapenos, brine, mustard and garlic together in a small bowl. Set aside until ready to serve.
• Combine the chuck and brisket in a medium bowl and using 2 forks, "pull" the meat apart, breaking up any clumps and combining the two meats together. This will seem counterintuitive but it will blend the meats together without compacting them. Divide into 4 equal portions and form balls (about the size of tennis balls) being careful not to compact or overwork the meat -- do not form patties.
• Heat 2 tablespoons of the oil in a large cast-iron skillet over medium-high heat. Add the onions and season with salt and pepper; cook, tossing occasionally, until golden browned, 6 to 8 minutes. Sprinkle with the sugar and toss until caramelized, about 1 minute. Transfer to a plate.
• Increase the heat to high and heat the same skillet until very hot. Add the remaining oil (or 1 tablespoon oil, if working in batches), swirling to coat.
• Working in batches if necessary, place balls in the skillet and smash flat with a metal spatula using the handle of a wooden spoon to press down on the spatula to form 4-inch patties (you want to see craggy edges). Season liberally with salt and pepper and cook, undisturbed, until the outer edges are brown, 1 to 2 minutes. Flip the patties, season with salt and pepper and top each patty with a slice of cheese. Cook until the cheese droops and the burgers are medium-rare, about 1 minute.
• Serve the patties on the toasted buns with the spicy special sauce, griddled onions, lettuce and tomatoes.