There's nothing like a reuben sadwich with its layers of sauerkraut, corned beef, and swiss cheese on some buttery rye bread. This one is kicked up with a spicy sauce.
Make sauce. Stir all ingredients together in a small bowl.
Spread about 2-3 teaspoons of spicy sauce on each piece of bread.
On half of the bread slices place about 1/4 to 1/3 cup sauerkraut.
On top of the sauerkraut, layer the corned beef, evenly distributing it among the 4 sandwiches.
Place 3 slices of swiss cheese on top of the corned beef for each sandwich. Top with remaining bread slices.
Heat a nonstick skillet or grill pan over medium heat. Place 2 tablespoons of butter on the hot pan and use a knife to spread it around the pan until it is completely melted.
Place the sandwiches on the pan and cook until the bottom is nicely toasted.
As you flip each sandwich, place a piece of the remaining butter on the pan and coat the pan well with it before setting the sandwich back down. Continue to cook until cheese melts, turning the heat to low if necessary.
Notes
To prevent a soggy sandwich, squeeze the sauerkraut with some paper towels to get as much liquid out as possible. If my corned beef is cold from the refrigerator I will usually heat it in the microwave for a few seconds or warm it in the pan I will be cooking the sandwiches in. The cheese will melt much more easily and your sandwich will be more of an even temperature all the way through if you're not starting with cold meat in the middle.