Lightly mist a small skillet with cooking spray and bring over medium heat. Add the spinach and cook for about a minute. Add the minced garlic and cook for another 30 seconds to a minute until the spinach is wilted.

In a mixing bowl, combine the spinach & garlic with the cream cheese, sour cream, Parmesan, ¼ cup of the Mozzarella, artichokes, black pepper and red pepper flakes. Stir until well combined.

Butter one side of each piece of bread with ½ tablespoon of butter each. Place two slices butter side down on a flat skillet. Sprinkle both slices with 2 tablespoons of shredded Mozzarella each. Spread the spinach & artichoke dip from step 2 evenly over the Mozzarella layer on each slice. Sprinkle the top of each with the remaining Mozzarella (2 tablespoons each). Place the reserved slices of bread, butter side up, on top of each sandwich.

Bring the skillet over medium heat and cook for about 2 ½-3 minutes until golden on the bottom. Flip the sandwiches (carefully!) and cook for another 2-3 minutes until golden on both sides.