Blend together flour, shortening and salt. Put the egg yolk in measuring cup and fill balance of cup with milk to measure 2/3 cup. Add to flour mixture. Mix like pie crust. Divide dough in half and roll out to fit 10 1/2 x 15 jelly roll pan. Peel, core and slice apples and arrange over crust. Mix together the sugar, cinnamon, flour and tapioca. Sprinkle over the apples. Roll out remaining dough and put on top of apples. Beat the egg white until stiff and spread over top crust. Sprinkle 1 or 2 tablespoons sugar over egg whites. Bake @450 degrees for 10 minutes. Reduce heat to 400 degrees and bake 20-25 minutes.