Heat a skillet over medium heat.
Butter one side of each bread slice evenly.
Place one slice of bread butter-side-down on the skillet.
Layer the mozzarella cheese slices on top of the bread in the skillet.
Top with the second slice of bread, butter-side-up.
Grill for about 3 minutes or until the bottom is golden brown and crispy.
Carefully flip the sandwich and grill the other side for another 3 minutes, until golden brown and the cheese is melted and gooey.
Remove from skillet and let cool slightly.
Cut the sandwich diagonally into two halves and stack slightly offset on a plain white plate.