Cut around a third off the pastry and set aside. Sprinkle the base of a 20cm shallow pie dish with the semolina or ground rice. Roll out the bigger piece and use to line the pie dish, leaving some overhang round the edges.
Preheat the oven to 190C/fan oven 170C/gas mark 5. Combine the flour and sugar in a large mixing bowl. Stir in the apples with then the lemon zest and juice. Spoon the apples into the pastry shell. The pie should be very full as the apples will sink down on cooking. Brush the rim with milk or water.
Roll out the top and carefully lift over the pie. Trim round the edges, which will help to seal in the filling. Use any trimmings to cut leaves to decorate the top. Brush all over with milk, sprinkle with the sugar and cut 3 holes in the middle to let out the steam. Bake on a baking tray for around 40 minutes until the pastry is golden and crisp. Let it sit for 5-10 minutes before slicing and serving.