1.Preheat oven to hot, 200°C (180°C fan-forced). Line two oven trays with baking paper.
2.Place rhubarb in a baking dish and sprinkle with half the sugar. Bake 15-20 minutes, until tender. Stir apple through.
3.Meanwhile, in a small bowl, combine breadcrumbs, remaining sugar, custard powder and vanilla.
4.Layer 3 sheets of pastry on a clean bench, brushing each with butter. Arrange one-third apple and rhubarb mixture lengthways along long edge of pastry. Sprinkle with one-third breadcrumb mixture. Roll up pastry to enclose filling, pinching ends closed. Place on a tray and brush with butter. Repeat with remaining ingredients.
5.Bake 15-20 minutes, until crisp and golden. Cool completely. Trim ends and cut each log into 5cm rolls. Dust with icing sugar to serve.
Accompany strudel rolls with ice-cream or thick cream, if desired.Note