Add ice, mint, simple syrup and lime juice; muddle until leaves are bruised and fragrant. Add rum; shake vigorously to blend and chill. Pour into glass; stir in soda water. Garnish with raspberries and mint sprigs.
Simple Syrup: Add 1 cup of water and 1 cup of granulated sugar to saucepan. Heat until clear and sugar is dissolved. Makes 1-1/2 cups. For extra flavor, add zest from your lime to simple syrup (before juicing it for cocktail.)