In a small saucepan bring water to a gentle simmer. Gradually stir in semolina; add sugar, rosewater and mastic. Cook, stirring, over low heat, about 5 minutes or until thickened. Transfer custard to small heatproof bowl; cover surface of custard with plastic wrap. Cool 1 hour.

Cut each pastry sheet in half, then cut each half into three rectangles. Roll one rectangle on floured surface until 12cm square. Place 1 level tbsp custard in centre of pastry; brush edges with egg. Fold two opposite edges of pastry over filling to enclose; brush the other two opposite edges with egg and fold to almost meet in the centre. Repeat with remaining pastry and custard.

In a large saucepan or wok, heat oil and deep-fry pastries, in batches, until browned lightly and crisp. Drain on absorbent paper.

Serve immediately, dusted with sifted icing sugar.