In a saucepan over medium heat, combine fresh or frozen blueberries with sugar, stirring gently. Cook for 5-7 minutes until the mixture thickens into a jammy consistency.

Spread a generous layer of cream cheese or brie on one side of each slice of sourdough or white bread. Layer the shredded mozzarella or fontina directly on top of the cheese, followed by a spoonful of the blueberry mixture.

Take the remaining slices of bread and place them, cream cheese side down, on top of the blueberry and cheese-laden slices. Press down gently to secure the fillings.

Heat a skillet over medium-low heat while buttering the outside of each sandwich. Place the sandwiches in the skillet, cooking for 3-4 minutes on each side.

Remove the sandwiches from the skillet and let them rest for 1-2 minutes. Slice each sandwich diagonally, revealing the melty cheese and fruits inside. Finish with a sprinkle of flaky sea salt.