Beef Sliders with Griddled Onions

Steps

1. 1Combine the garlic powder, pepper, and 1/4 teaspoon of the salt in a small bowl. Set aside.
2. 2Combine the onions and the remaining 2 teaspoons salt in a bowl and set aside until you can see liquid pooling in the bottom of the bowl, 15-20 minutes. Drain in a fine mesh sieve set over a medium bowl, pressing on the onions to remove additional liquid. You'll need the onions and the juice.
3. 3Place the ground beef in the middle of a 12x16-inch sheet of parchment. Cover the meat and the entire piece of parchment with plastic wrap. Roll out the meat with a rolling pin (the plastic is between the meat and pin) until it forms an even, 2-3 millimeter thick rectangle completely covering the parchment paper.
4. 4Carefully peel off the plastic wrap and evenly spread the mustard over the meat, then season with the garlic powder mixture. Pick up the edge of the parchment and fold the meat in half, widthwise. Press the meat together to seal the two layers and square off the edges as best as you can. At this point, the meat should be about 1/4-inch thick. Slide onto a sheet pan and refrigerate for 10 minutes.
5. 5When the meat has had time to firm up in the refrigerator, fold back the top layer of parchment and use the pizza cutter to portion the meat into 8 (3x4-inch) rectangles. Use a spatula to gently separate the patties.
6. 6Set your electric griddle to 350℉.
7. 7Spread the onions out on the griddle in an even 12x8-inch rectangle. Put the patties on top of the onions, resisting the urge to press them with your spatula. Pour over about 1 tablespoon of the reserved onion juice to create steam, then top each patty with a slice of cheese and the bottom half of a bun. Cover the griddle with foil (but do not seal) and let the burgers steam until cooked through and no longer pink, 3-5 minutes.
8. 8While the burgers steam, add the pickles and more mustard (as desired)to each bun top. Using a large spatula, pick up a burger-and-bottom-bun stack and place it on the top half of a bun. Repeat with the remaining burger stacks and bun tops until there's nothing left to build. Flip the burgers right-side up and consume in mass quantities.