Preheat the oven to 400 degrees.
To make the pie:
1) Combine the first measure of flour, salt and shortening using a pastry blender until the mixture resembles coarse crumbs, then stir in the water a little at a time, using a fork, and form the dough into a ball.
2) Roll out the pastry dough on a lightly floured board. Roll to an 11" or 12" diameter and fit into a 9" pie pan fluting the edges.
3) Combine the sugar, the second measure of flour, the cinnamon, the nutmeg and the lemon juice in a large bowl then toss the apple slices in the mixture and arrange them in the pie crust. To make the topping:
4) Combine the sugar and flour in a bowl and cut in the butter using a pastry cutter then sprinkle the topping over the apple filling.
5) Place the pie in the LARGE paper bag and place the paper bag on a baking sheet and loosely fold the open end of the bag under. Bake until the apples are tender (50-60 minutes).
6) Carefully remove the pie from the bag ~ CAUTION: WATCH OUT FOR THE STEAM COMING OUT OF THE BAG!
7) Serve warm with generous portions of vanilla ice cream.