In a saucepan over medium heat, combine 1 cup of fresh or frozen blueberries with 2 tablespoons of sugar. Stir gently for about 5–7 minutes until the mixture thickens and turns a deep purple hue. Set aside to cool.

Spread a generous layer of cream cheese or brie on one side of each of the four slices of bread.

Layer 1 cup of shredded mozzarella or fontina cheese evenly over the cream cheese on two slices. Spoon the cooled blueberry mixture on top.

Butter the outsides of each sandwich with 3 tablespoons of butter. Heat a nonstick skillet over medium-low heat.

Place the sandwiches in the pan and cook for 3–4 minutes on one side until golden brown and the cheese begins to melt. Flip and cook for another 3–4 minutes.

Let the sandwiches rest for 1–2 minutes before serving. Optionally, sprinkle with flaky sea salt before cutting and serving warm.