Heat sugar with 200 ml (approximately 3/4 cup) of water and simmer for about 15 minutes, then let cooling. Set aside some raspberries. Mix the rest of the raspberries with lemon juice, puree, and place through a fine sieve. Mix with sparkling wine and sugar syrup, fill everything in a shallow metal bowl. and freeze for at least 4 hours. Stir often with a fork to prevent the formation of large crystals, or finish in an ice cream machine.
Scoop sorbet balls, fill in glasses and serve garnished with mint and berries.