Roll out the pastry on a lightly floured worksurface until about 40cm x 30cm and the thickness of a £1 coin. Cut into four even rectangles. Spoon the chicken curry onto one half of each rectangle, leaving a 2cm border at the edges, and top with the mango chutney. Brush the edges with some of the beaten egg and fold over the pastry to seal. Crimp the edges, sealing well to prevent them bubbling out during cooking, and transfer to a baking sheet lined with baking paper. Chill until ready to bake, or freeze.