1 Place the rhubarb, sugar and water in a pot and simmer for about 10 minutes until soft. Puree the rhubarb and leave to cool.
2 Add the lemon juice and the sparkling wine and place in a freezer for around 3 hours. Stir with a fork every now and again to keep the mixture grainy. It should not be creamy like a sorbet.
3 Transfer to chilled glasses, garnish with the mint and serve.