PLACE butter, flour, and salt for the base in the food processor; pulse ingredients to a crumb consistency.
ADD a tablespoon of water and pulse again; repeat this process until a homogeneous dough is obtained.
COVER the dough with plastic wrap and refrigerate for one hour.
COMBINE apples with brown sugar, cinnamon, lemon juice, and flour; set aside.
Add walnuts to the food processor with brown sugar, flour, butter, and salt; pulse until a sandy mixture with medium walnut pieces is obtained.
SPRINKLE flour on the work surface, roll out the dough, line a tart pan, press edges well, and trim excess.
FILL tart with apple mixture without adding apple juices; top with pecan topping.
COVER apple pie with foil and bake at 180°C for 25 minutes; remove foil and bake for 20 minutes more.
REMOVE the apple pie with walnut topping from the oven and let stand for 30 minutes before unmolding and serving.
