Preheat oven to 180°C, 350°F, Gas Mark 4.
Brush both sides of the bread slices with butter and place them on a baking sheet. Bake for 5 minutes.
In a pan, stir together the cranberries, balsamic vinegar, water, sugar, and Rosemary. Simmer a low heat 10 minutes.
Top each bread with a slice of brie and a spoonful of the herbed cranberry mixture.