Heat a non-stick pan over medium heat.

Butter the outside of each slice of bread. Spread basil pesto on the inside of each slice of bread. Place the mozzarella cheese slices on top of one piece of bread. Top with the other slice of bread. Sprinkle half of the Parmesan cheese on the outside of one side of the sandwich.

Place the sandwich, cheese side down, on the hot pan. Grill for 2 minutes or until Parmesan cheese is crusted and golden brown. Sprinkle the rest of the Parmesan cheese on the outside of the other side of the sandwich. Cook until golden brown and the cheese has melted, about 2 more minutes. Serve immediately.