In a small saucepan over medium heat, combine fresh or frozen blueberries with sugar. Cook for 5-7 minutes until the mixture thickens and becomes jammy, stirring occasionally.

Spread a generous layer of cream cheese or brie on one side of each slice of bread. On the cream cheese side of one slice, sprinkle shredded mozzarella or fontina cheese, then add the jammy blueberry mixture on top.

Place a skillet over medium-low heat and butter the outer sides of your assembled sandwich.

Carefully place the sandwich in the skillet, cooking it for 3-4 minutes until golden brown and crispy. Flip and cook the other side for an additional 3-4 minutes until the cheese has melted.

Remove the sandwich from the skillet and let it rest for a couple of minutes. Sprinkle flaky sea salt on top before slicing.

Slice the sandwich into halves or quarters and serve immediately with options like salad or soup.