Place the fruit, orange rind and juice, liqueur and 175ml water in a food processor and blend until smooth. I like to leave to seeds in but you can sieve your mixture if you prefer.
If you have an ice cream machine, churn the mixture until it starts to freeze, alternatively pour into a rigid container and freeze, stirring every 30 minutes or so until ice crystals start to form and it feels slushy.
Whisk the egg whites until stiff then gradually add the sugar beating until firm and glossy. Fold the meringue into the freezing fruit mixture and continue to freeze and stir until completely frozen. If making in advance, transfer the mixture to the fridge 30 minutes before serving.