Instructions

1. Drain 1 packed cup sauerkraut through a fine-mesh strainer. Heat 1 tablespoon of the vegetable oil in a medium cast iron or nonstick skillet over medium-high heat until shimmering. Add the sauerkraut and cook, stirring often, until just warmed through, about 1 minute. Transfer to a small bowl.
2. Heat the remaining 1 tablespoon vegetable oil in the same pan over medium heat until shimmering. Add 12 ounces sliced corned beef and cook, tossing occasionally with tongs or chopsticks to separate the slices, until just warmed through but not browned, about 1 minute. Transfer to a bowl or plate. Wipe the skillet clean with paper towels and set aside.
3. Cut 4 tablespoons unsalted butter into 8 pieces.
4. Lay 8 slices rye bread on a work surface. Spread 1 tablespoon Russian dressing on each slice. Place 1 slice Swiss cheese on each of 4 slices of bread. Divide the corned beef and sauerkraut over the cheese. Top each with a second slice of Swiss cheese. Close the sandwiches with the second slice of bread dressing-side down.
5. Heat the reserved skillet over medium-high heat. Add 2 pieces of the butter. When melted, swirl the pan to coat, then carefully add 2 of the sandwiches. Press down on the sandwiches with the back of a flat spatula to flatten slightly, then cook until deep golden-brown on the bottoms, about 1 1/2 minutes.
6. Add 2 pieces of the butter. Once melted, flip the sandwiches and cook until deep golden-brown on the second side and the cheese is melted, about 1 minute more. Transfer to a plate or cutting board. Repeat cooking the remaining sandwiches in the remaining butter. Serve with pickles if desired.