Butter slices of bread on both sides.
In a pan over low heat, add a slice of bread, 1/2 cup of both kinds of cheese, and top with another slice of bread.
Cook over low heat about 3 minutes on each side, using a weight to hold the sandwich down.
Remove the sandwich from the pan.
Grate more cheese to add to the pan (about 1/8 cup of each kind of cheese per side) and set the sandwich back down on top of the cheese.
Slowly remove from the pan creating a crispy cheese crust.
Repeat with the other side.