In a small saucepan over medium heat, combine your fresh or frozen blueberries with sugar. Cook for about 5–7 minutes, stirring occasionally, until bubbly and jammy.

While the blueberry mixture cools slightly, spread a layer of cream cheese or brie on one side of each slice of bread. On two slices, add shredded mozzarella or fontina cheese, then spoon the warm blueberry filling over the cheese.

Spread butter generously on the outside of each sandwich, covering evenly. Heat the skillet over medium-low heat.

Place the sandwiches in the heated skillet and cook for about 3–4 minutes on each side, pressing down gently with a spatula.

Once golden and the cheese is melted, remove from the skillet and let rest for 1–2 minutes before slicing and serving.