To make garlic butter mixture, combine together butter, minced garlic and parsley in a small bowl. Season with salt and pepper. Set aside.
Spread one side of a bread slice with one tablespoon garlic butter mixture. Repeat with the remaining bread slices. Set aside.
Place a frying pan over medium-low heat. Add 1 tablespoon butter. When butter starts to melt, place bread buttered side down in the pan.
Top with 2 tablespoons mozzarella. Top with another bread slice, buttered side facing upwards.
When one side is golden, flip over to cook the other side until golden. This will take about 4-5 minutes. Remove the toasted grilled cheese from pan.
Repeat with the remaining buttered bread slices, butter and cheese. Serve immediately.