01 - In a small mixing bowl, gently combine the fresh blueberries with honey and lemon zest if using.
02 - Spread the softened cream cheese evenly over one side of each bread slice using a butter knife.
03 - Sprinkle shredded mozzarella over two of the bread slices, on the cream cheese side.
04 - Evenly distribute the prepared blueberry mixture over the mozzarella-covered slices.
05 - Top with the remaining bread slices, cream cheese side facing inward, to form sandwiches.
06 - Spread softened butter on the outer sides of each assembled sandwich.
07 - Preheat a nonstick skillet or griddle over medium heat. Place the sandwiches in the skillet and cook for 3 to 4 minutes per side, pressing gently, until the bread turns golden brown and the cheese is fully melted.
08 - Remove from skillet, allow to cool for 1 to 2 minutes, slice in half, and serve warm.