Rub the butter into the flour and salt until it looks like rough crumbs, then add the ice water a spoonful at a time until the dough holds. Split in two discs and chill for 1 hour.
Toss the apples with the sugar, cornflour, cinnamon and lemon juice.
Heat the oven to 200°C. Roll out one disc to line a 23 cm pie dish and pile in the apples.
Roll the second disc, cut it into strips and weave a lattice over the top. Crimp the edges and brush with egg.
Bake for 20 minutes, then turn down to 180°C and bake for another 40 minutes until the filling bubbles through the lattice.
Cool for at least 2 hours before slicing, so the filling sets.
1 h 15
