Butter 6 x 7.5cm/3in dariole moulds (or a 22cm/9in ovenproof dish if you want to make one large pie).
Roll out two-thirds of the pastry on a floured work surface using a rolling pin. With a pastry cutter the size of the dariole moulds, cut out six discs large enough to line the dariole moulds; line the bottom and sides of the buttered moulds with the pastry discs (or if making one pie, cut out a large circle of pastry to line the buttered dish). Transfer to the fridge to chill.
Place the sugar, lemon juice and lemon zest into a bowl.
Peel, quarter and core the apples, then slice them thickly into the bowl with the lemon and sugar. Mix together.
Heat a pan over a medium heat. Add the apple mixture, the butter and the cinnamon (if using) and stew for 3-4 minutes. Add the blueberries and cook for a few more minutes, before removing from the heat to cool.
Preheat the oven to 200C/400F/Gas 6.
Fill the pastry-lined dariole moulds or pie dish with the cooled apple and blueberry mixture.
Roll out the remaining pastry on a floured work surface and cut out discs a little bigger than the dariole moulds or pie dish. Place the pastry on top of the the dariole moulds or pie dish and seal the edges well. Make a small hole in the top to allow the steam to escape.
Make decorations (such as leaves) by cutting out any pastry trimmings with a sharp knife and stick them on with a little water. Brush the pastry lids with a little lightly beaten egg then dredge with caster sugar.
Bake for 15 minutes, until the fruit is tender and the top is golden-brown. Serve hot with clotted cream