Preheat oven to 200 degrees C. Peel the apples, grate one with a cheese grater, using the biggest slats on the grater, and thinly slice the rest. Mix the apples, sultanas and sugar together and set aside.
Roll the thawed pastry with a rolling pin slightly and place it on a greased baking tray. Spoon the apple mixture down the middle of the pastry lengthways, leaving a 4 cm gap at each end.
Fold the pastry and seal the long and short edges by brushing them lightly with water an pressing together
Beat the egg and milk together till thoroughly mixed then brush this on top of the pastry. Bake for 35-40 minutes.