Sharbat-e reevas (rhubarb-rosewater sherbet)

1.Combine the rhubarb and sugar in a large, heavy-based saucepan and macerate for 1½ hours.

2.Add 1 cup (250ml) water and bring to the boil over a low heat, stirring until the sugar has dissolved. Increase the heat and simmer gently for 20 minutes. Strain through a piece of muslin or clean Chux, then return the strained juice to the pan and add the lime juice. Boil until the syrup is thick (10-15 minutes). Remove from the heat and cool. Stir in the rosewater and rose petals, if using, and transfer to a sterilised bottle, then seal and store in a cool place. Syrup will keep for 3 months.

3.To serve, mix 1 part syrup with 3 parts chilled water or soda water. Top with ice, garnish with rose petals, if using, and serve.