Toast the sandwich loaf slices in a toaster. Spread butter to the inner side of a slice of sandwich loaf. Put a slice of kasseri cheese on it. Add the ham and burger cheese on it. Cover with the other slice of sandwich loaf. Add the kasseri cheese which is separately grated and mixed well with the egg yolk on the slice of sandwich loaf. Bake the toast in the oven until the cheese melts and it turns golden brown. When it is baked, serve hot. Good appetite!