Break chocolate into 2 pieces. In a bowl whisk together eggs, vanilla, and milk. Using a 3-inch heart-shaped cutter cut a heart shape from each slice of bread. Place a piece of chocolate on top of one of the pieces of bread and gently press another piece on top, pinching the edges. Repeat the procedure with other 2 pieces of bread. Dip bread into egg mixture, making sure they are soaked. Heat the butter in a non-stick skillet over moderate heat until it begins to foam, add the stuffed bread hearts and cook them, turning them once for 2 to 3 minutes per side or until they are nicely browned. In a bowl mash 3/4 of the raspberries and stir in the sugar. Stir in the remaining berries. Transfer the browned hearts to a plate and top with the raspberries. Dust with confectioners' sugar and garnish with mint.