1 Add the orange juice to the sugar, vanilla extract, and 150 ml water. Bring to the boil and allow the sugar to dissolve, then take off the heat and leave to cool.
2 In a mixer, blend the orange juice mixture, the melon flesh and the orange blossom water to a fine purée. Whisk the egg white to soft peaks and stir into the fruit purée.
3 Finish in an ice cream machine, or tip into a flat container and freeze for at least 3 hours, stirring thoroughly every 30 minutes.
4 Serve in scoops, with mango if desired.