Heat sugar with 200 ml of water to simmer for about 15 minutes, followed by cooling. Thaw strawberries, put some nice berries aside. Puree berries with lemon juice, strain through a fine sieve and mix with sparkling wine and sugar syrup. Put everything in a shallow metal bowl. Freeze at least 4 hours, stirring often with a fork to prevent the formation of too large crystals.
Serve the sorbet with strawberries.