01 - In a small mixing bowl, gently combine fresh blueberries with honey and lemon zest, if using.
02 - Evenly distribute softened cream cheese on one side of each bread slice using a butter knife.
03 - Sprinkle shredded mozzarella cheese on top of the cream cheese on two bread slices.
04 - Spoon the prepared blueberry mixture evenly over the mozzarella cheese.
05 - Place the remaining bread slices, cream cheese side down, on top to form sandwiches.
06 - Spread softened butter over the outer sides of each sandwich.
07 - Preheat a nonstick skillet over medium heat. Place sandwiches in the skillet and cook for 3 to 4 minutes per side, pressing gently, until the exterior is golden brown and the cheese is thoroughly melted.
08 - Remove sandwiches from the skillet, allow to cool slightly, cut in half, and serve warm.