Set up the barbecue for baking (in-direct method) and pre-heat to approximately 200°C.
On a floured surface, roll out two-thirds of the pastry and use it to line a 23cm tart tin, leaving a slight overhang and keeping any pastry scraps. Chill the tart for 10 minutes. Prick the base lightly with a fork, then fill with baking paper and baking beans. Place on barbecue, remove the beans and paper, and then bake for 10 minutes until golden. Remove from the barbecue.
Place the apples into a large saucepan, with 2 tbsps water and stew for 10-12 minutes, until al dente. Toss in the berries, sugar, cinnamon and 2 tbsps flour with a pinch of salt and pile it into the pastry case.
Roll the remaining pastry and trimmings together into a square roughly 30 x 30cm. Cut out 8 strips of pastry about 3 x 30cm. Weave the strips of pastry evenly over the fruit to create a lattice pattern and push them into the edge of the tart. Trim the overhang of pastry; brush the lattice heavily with the egg, then scatter generously with more sugar.
Bake (in-direct method) on the barbecue for 1 hour until brown and bubbling. Leave the pie to cool for 30 minutes until no longer scorching. Scatter with more sugar, slice and serve.