Heat the cast iron skillet over medium heat.
While the skillet heats up, spread one teaspoon of butter on one side of a chaffle and place it in the pan butter side down.
Place the cheese slices on top of the chaffle in the pan.
Top the cheese with the second chaffle and spread the remaining teaspoon of butter on the outside.
Cook the sandwich on the first side until it starts to sizzle and brown in the butter for about two minutes. Cover the pan with a lid to help the cheese melt faster, if desired.
Flip the grilled cheese over and toast the other side until the cheese is melted and the chaffle is toasted.
Remove from the heat and enjoy.