Sift together flour, salt and sugar in large, chilled bowl.
Using a pastry blender cut butter and shortening into flour until crumbly with small bits of fat still intact.
Sprinkle vinegar and smallest amount of water over the flour mixture.
Mix with fork just until ingredients come together, add remaining water if needed. Large pieces of dough should stick together when patted.
Pat into a flat ball, wrap in plastic wrap and refrigerate for at least 1 hour.
Filling
In large bowl toss together sliced apples, pie spice and brown sugar.
Assembly
Preheat oven to 425°F.
Cut cold dough into two pieces. Keep one half refrigerated while preparing the other.
Roll out dough into a 10 inch circle, about 1/4 inch thick.
Arrange half of sliced apples (3 cups) in center of dough leaving a 1 1/2 inch border all around. You can make a rustic pile of apples or make neat concentric circles of apple slices.
Fold border of dough up and around the apples. No need to be fussy - remember, you're going for a rustic look! Just be sure there are no cracks that would cause fruit juice spillage while baking.
Use a pastry brush to apply a coating of milk on pastry edges.
Sprinkle with sugar. Raw sugar or sugar with large crystals is best, but any kind will do.
Repeat process with the remaining dough and apples.
Place in oven for 25 to 30 minutes.
Cool for as long as possible before enjoying with ice cream or freshly whipped cream
Notes
If the top is getting too dark, cover with aluminum foil.