Line a large baking tin with a sheet of parchment paper.
Sandwich 1:
Spread the butter on top of the bread slices. Cover generously with grated cheese.
Optionally mix together the lightly beaten egg with the grated cheese before spreading the mixture on top of the bread.
Sandwich 2:
In a bowl mix very well the crumbled cheese and the egg.
Spread the butter on the bread slices. Spread on top the cheese mixture, dividing it evenly between the slices.
Bake the sandwiches for about 15-20 minutes in the oven, with only the top heat on. They are ready when the cheese becomes golden-brown.
Serve immediately.
Notes
The traditional Bulgarian yellow cheese is called kashkaval. It can be substituted by cheddar, gouda or other similar kinds.
The Bulgarian white cheese sirene is similar to feta but made of cow milk. You can substitute it with feta, ricotta or cottage cheese.
Don't add too many or too strong spices to these sandwiches. Black pepper or savory are simple and good options. You can also sprinkle Homemade Sharena Sol.