01 - In a small saucepan over medium heat, combine balsamic vinegar and honey. Simmer gently for 3 to 5 minutes, stirring occasionally, until the mixture thickens. Remove from heat and allow to cool slightly.
02 - Spread softened butter evenly on one side of each bread slice. Place two slices, buttered side down, onto a clean surface.
03 - Layer sliced brie evenly over both slices of bread, followed by shredded sharp white cheddar and halved blackberries. Drizzle each with one teaspoon of balsamic glaze.
04 - Cover each with a remaining bread slice, buttered side facing up, to form sandwiches.
05 - Heat a nonstick skillet or griddle over medium heat. Place sandwiches in the skillet and cook for 3 to 4 minutes on each side, pressing gently, until the bread is golden brown and the cheese melts.
06 - Remove from heat, rest sandwiches for 1 minute, then slice and serve while warm.