Heat a griddle or pan.
Spread the butter on each side of the bread slices.
Lay two bread slices with buttered side down on the heated griddle or pan.
Arrange two Swiss cheese slices on top of each bread.
Equally place the corned beef deli on top of the cheese for both breads and then top with sauerkraut.
Spread mayonnaise on the other side of the remaining 2 bread slices (one side has mayo and the other has butter). Top the remaining slices of bread over the sauerkraut (mayo side down).
Turn the sandwich over to heat the other side. Let it stay until the bread turns golden brown.
Slice the bread in the middle and serve.
Share and enjoy!