Slather butter on the outside of two pieces of Sourdough bread.
In a preheated pan just under medium heat add the bottom piece of bread, most of the shredded mozzarella to the bread, followed by crumbled bacon (you can add as much or as little as you'd like).
Top the bacon layer with a slice of American cheese. Followed by the top piece of bread.
Cook until golden brown then flip. Just before you're ready to remove from the pan. Top with a pinch of mozzarella and flip again so the cheese is now face down in the pan.
Allow the cheese to get crispy and brown which takes about 45 seconds. Top the other piece of bread with a pinch of mozzarella and repeat this step.