In a bowl, combine flour and salt; cut in shortening. Gradually add cold water, 1 tablespoon at a time, tossing lightly with a fork until dough forms a ball. Chill for 30 minutes. On a floured surface, roll half of dough into 10-in. circle. Place into a 9-in. pie pan.
In a bowl, toss apples with lemon juice. Combine sugar, flour, cinnamon, salt and nutmeg; add to apples and toss. Pour into crust; dot with butter. Roll out remaining pastry to fit top of pie; cut slits in top. Place over filling; seal and flute edges. Beat egg yolk and water; brush over pastry. Bake at 425° for 15 minutes. Reduce heat to 350°; bake 40-45 minutes more or until crust is golden and filling is bubbly.