Sift together:
3 c flour
2 tsp baking powder
1 tsp salt
½ c sugar

Cut in 1 cup shortening

Mix and add:
1 egg, beaten
½ c cold water

Put dough in refrigerator and chill. On well floured counter, roll out 2/3 of dough and fit into a 15x10x1 inch jelly roll pan. Roll out remaining dough for top, and set aside

Filling:
Peel and slice 8 or 9 large granny smith apples.

Mix with:
1 c sugar
2 Tbsp dry tapioca
½ tsp cinnamon
dash of nutmeg

Spread filling over dough in pan. Dot with butter. Top with remaining dough but DO NOT seal edges. Prick all over top with a fork. Bake at 350 degrees for 1 hour. While still warm, drizzle with a powdered sugar glaze.