Preheat oven to 220°C (200°C fan-forced). Grease deep 23cm square cake pan; line base and sides with foil, extending foil 10cm over sides.

Place pastry sheets on separate greased oven trays. Bake about 15 minutes; cool. Flatten pastry with hand; place one pastry sheet in pan, trim to fit, if necessary.

Meanwhile, combine rhubarb, sugar and the water in large saucepan; cook, covered, stirring occasionally, until rhubarb mixture is pulpy. Cool.

Combine extra sugar, cornflour and custard powder in medium saucepan; gradually stir in milk until smooth. Add butter; stir over heat until mixture boils and thickens. Reduce heat; simmer, stirring, about 5 minutes or until custard is thick and smooth. Remove from heat; stir in egg yolk, extract, cream and rhubarb. Tint custard with pink food colouring. Spread warm custard mixture over pastry in pan. Top with remaining pastry, puffed-side down, trim to fit if necessary; press down lightly.

To make orange icing; sift icing sugar into small heatproof bowl; stir in enough of the juice to make a firm paste. Stir icing over small saucepan of simmering water until spreadable.

Spread pastry with icing; refrigerate slice 3 hours or overnight.