In a small saucepan, combine sugar and water. Bring to a boil, stirring until sugar is dissolved. Remove from heat.
In a blender or food processor, combine raspberries with sparkling wine, crème de cassis, and sugar syrup until smooth. Strain purée through a fine sieve, pressing hard on the solids. Add lemon juice. Chill until mixture is cool, then freeze in an ice cream machine.