* Combine 1/4 cup sugar and 1/4 cup water in a small, heavy saucepan, and bring to a boil, stirring until sugar dissolves. Add 2 mint sprigs to pan; let stand 5 minutes. Remove mint and discard. Combine sugar mixture, 3 cups fresh raspberries, and 2 tablespoons fresh lemon juice in a blender, and process until smooth. Strain mixture through a sieve over a bowl, and discard solids. Spoon 3 tablespoons raspberry mixture into each of 6 wineglasses; top each serving with 1/2 cup chilled Champagne.