1. In a small saucepan over medium heat, combine the blueberries, honey, lemon zest, and a pinch of salt. Cook for about 5 minutes, stirring occasionally, until the blueberries start to burst and the mixture thickens slightly. Set aside to cool.
2. Lay out the bread slices and spread butter evenly on one side of each slice.
3. On the unbuttered side of two slices, layer the brie and cheddar cheese evenly. Spoon the blueberry mixture over the cheese layers.
4. Top with the remaining slices of bread, buttered side facing out.
5. Heat a skillet over medium-low heat. Place the sandwiches in the skillet and cook for 3-4 minutes on each side, or until the bread is golden brown and the cheese is melty and gooey.
6. Remove from the skillet and let them cool for a minute before slicing. Enjoy the gooey, sweet-savory bliss!

One tip from my childhood: cover the skillet with a lid for the last minute of cooking to ensure the cheese melts perfectly without burning the bread.