Cook the cranberries in a saucepan with the sugar, orange rind and juice and the measurement water for 10 minutes, stirring occasionally until the cranberries are soft. Mix the cornflour to a paste with a little extra water, add to the cranberries and cook for a few minutes, stirring until thickened, then leave to cool.
Cut the pastry in half, roll out one half on a lightly floured surface and trim to a 20 × 25 cm (8 × 10 inch) rectangle, then transfer to a buttered baking sheet. Brush the egg in a border around the edge of the rectangle, then pile the cranberry mixture in the middle.
Roll out the remaining pastry a little larger than the first and drape over the cranberries. Press the pastry edges together to seal well, then trim the top pastry layer to match the lower one. Knock up the edges of the pastry, then flute (see
Brush the top with egg, then bake in a preheated oven, 200°F (400°F), Gas Mark 6, for 25–30 minutes until well risen and golden brown. Leave to cool for 30 minutes.
Mix the icing sugar with enough of the orange juice to make a smooth icing that just falls from a spoon, then drizzle randomly over the pie to decorate and sprinkle with the grated orange rind. Set aside for 20 minutes or until the icing is set, then cut into strips to serve.