01 - In a small saucepan over medium heat, combine balsamic vinegar and honey. Simmer for 3 to 5 minutes until thickened, then set aside to cool slightly.
02 - Spread softened butter on one side of each bread slice. Lay two slices, buttered side down, on a clean surface.
03 - Evenly layer brie slices over the bread, top with shredded cheddar and halved blackberries. Drizzle each sandwich with one teaspoon of the balsamic glaze.
04 - Top each with the remaining bread slices, buttered side up.
05 - Heat a nonstick skillet or griddle over medium heat. Place assembled sandwiches in the pan and cook for 3 to 4 minutes per side, pressing gently, until bread turns golden and cheese is melted.
06 - Remove sandwiches from heat and let rest for 1 minute. Slice and serve warm.