1 Wash and dry the lemon balm and put into glasses.
2 Cut off four slices of lime and put into the glasses. Squeeze the rest of that lime and the second lime into a saucepan.
3 Combine with the grape juice and sugar and bring to the boil. Boil for 4 minutes, stirring, then test for setting point.
4 Add the Grappa, stir well, and pour into the glasses. Leave to cool briefly and then chill for at least 2 hours. Alternatively pour into jam jars, seal well, stand the jars on their heads and leave to cool.