Smash Sliders 6 Steps
Start by caramelizing your onions. In a cast iron pan, heat 2 tablespoons neutral oil over medium heat. Add onions, season with a pinch of salt and cook, stirring often (keep your eye on them, you don't want your onions to burn) until soft and dark golden brown (20-30 minutes). You can add a splash of water throughout the cooking process to further soften the onions and if the onions appear to be burning, you can turn the heat down slightly. Season again with salt. Once caramelized to your liking, remove from heat and set aside in a small bowl.
On two large plates, start forming your patties. Take a small handful or roughly 1/4 cup of ground chuck and form into a rough ball, smash into a thin patty with your hands (remember, the patties will shrink quite a bit when cooked, so take this into account and adjust accordingly depending on your size preference). Place on plate and season both sides generously with salt and pepper. Continue until you have 24 individual patties (2 per slider) -- you will have ground chuck leftover, the rest can be placed in a freezer bag and stored in your freezer.
Make your special sauce. In a small bowl, whisk together 1/2 cup mayo, 4 tablespoons ketchup, 4 tablespoons mustard, 3 teaspoons of liquid from pepperoncini jar, 1 medium pickle cut into a small dice and season with salt and pepper. Taste and adjust according to preference. Set aside. Slice a few dill pickles for garnish, set aside.
Unwrap cheese slices and cut in half on the diagonal. Set aside on a plate. Cut your slider buns in half if not pre-cut, set aside.
Turn the oven on to 350°F. Wrap buns in tin foil and reheat until warm. Set a large sheet tray to the side. To cook your patties, heat a large cast iron pan over medium heat. Add enough neutral oil just to coat the bottom of the pan, swirling to evenly disperse the oil. Cooking in batches, add roughly 8 patties to the hot pan at a time. Dollop a small amount of yellow mustard to each top of the patty. Cook for 1-2 minutes or until a nice crust forms. Flip patties and top each with cheese. Let second side cook for an additional 30-45 seconds while cheese melts. Once cooked, remove onto sheet tray, stacking one patty onto the other. You should have 4 double burgers now. Repeat this process until burgers are cooked, pouring residual grease from pan after cooking each batch (no need to add more oil, your pan should be seasoned enough).
Place your sheet tray in the oven to reheat patties while you begin to assemble. On a large platter arrange the warm buns. Spread secret sauce on both bottom and top bun. When patties are heated back up again, place on top of bottom bun, top with caramelized onions, chopped pepperoncini, sliced dill pickles, bacon and top bun. Serve immediately!