The Juiciest Juicy Lucy

In a small saucepan, add lager and sodium citrate and bring to a simmer over medium-high heat, whisking occasionally to dissolve sodium citrate. Once simmering, whisk in the cheese, then lower heat to medium-low and cook, whisking frequently, until cheese melts into a pale, uniform paste, 3 to 5 minutes.

Remove prepared baking pan from the oven and pour cheese sauce into the warmed pan. Working quickly, tilt the pan to distribute the cheese in a thin, even layer (use a small offset spatula to spread if necessary). Once spread, refrigerate the pan until the cheese is firm, about 15 minutes. Cover and return to the refrigerator until ready to use. (You can leave the cheese in the pan or remove the cheese, still on the parchment, from the pan and place it in a large zipper-lock bag, or wrap it in plastic wrap.)

When ready to make the burgers, remove cheese from the refrigerator and use a 3 ½- round biscuit cutter or drinking glass to punch out 4 cheese rounds.

While cheese cools, in a 12-inch cast-iron skillet, melt butter over medium heat. Add onions and cook, stirring occasionally, until softened and beginning to caramelize, 10 to 15 minutes. If onions are beginning to burn before softened, add a splash of water (or, even better, a splash of the beer you used to make the beer cheese). Season with salt and pepper to taste and transfer to a bowl. Reserve the cast-iron skillet for cooking the burger.

Remove beef from the refrigerator 20-30 minutes before cooking, to give it time to warm to room temperature. Add it to a medium mixing bowl. In a separate small bowl, combine gelatin and 1 tablespoon water, mix well, and immediately pour over the beef. Mix into the beef thoroughly but gently, taking care not to overwork it. Shape the beef into eight 3-ounce balls—two per burger. Place each ball, one at a time, between two sheets of plastic wrap or parchment, and flatten it with the bottom of a heavy skillet, pressingly evenly and firmly, until the patties are about 5 inches wide and about 1/4-inch thick.

Place 1 flattened patty on a plate or cutting board, and place 1 beer cheese round (or two 3½-inch American cheese rounds) in the middle of each patty. Lay a second patty over the top and crimp the edges of the patties together. Carefully flip the burger and crimp the edges together on other side, taking care to seal the entire perimeter. Then, gently press the sides of the patty in to form a burger about 4-inches wide and 1/2-inch thick. Repeat until finished. Transfer flattened patties back to a large plate and refrigerate until firm to the touch, 15 minutes, or up to 24 hours.

In the now-empty cast-iron skillet, heat 1 teaspoon oil over medium-high heat until smoking. Season the patties generously with salt and pepper on both sides. Carefully transfer the burgers to the skillet and cook until well browned on both sides, 2 to 3 minutes per side. (Don't use a thermometer, which will liberate the molten cheese inside.)

Transfer the burgers to a plate, lower the heat to medium-low, and toast the buns in skillet, face-down, in two batches if necessary. Rest the patties for 5 minutes to cool the molten cheese inside slightly. Then, assemble the burgers: bottom bun, onions, patty, 3-4 pickle slices, top bun. Careful with that first bite.