Sift flour and place in a food processor. Add the diced butter and whizz to form crumbs. Add 4-5 tbsps cold water and pulse to form a firm pastry. Remove from the bowl, roll into a ball, wrap in clingfilm and chill for half an hour.
Place the sultanas (if you're using them), sugar and lemon zest into a large bowl. Peel, core and thinly slice the apples, adding them to the bowl as each one is done. Sprinkle over the spice and the flour.
Preheat the oven to 200°C, 390°F. Roll out two thirds of the pastry and use to line a 23-24cm pie dish, leaving any excess pastry to overhang the edge. Spoon the apple mixture into the dish and dampen the edge of the pastry along the rim with milk.
Roll the remaining pastry into a circle large enough to cover the filling and lay on top of the pie. Using a sharp knife, trim the excess pastry away and crimp the edges to seal. Brush the pie with milk and sprinkle with a little sugar. Make a slit or two in the top and bake for 35-40 minutes until golden brown. Leave to cool for at least 45 minutes before slicing and serving with cream or custard.
