In a large bowl, combine the apples, sugar, water, cinnamon, and nutmeg; toss to coat. Let stand for 15 minutes.
In a large bowl, combine the flour, baking powder, and salt; cut in shortening until crumbly. Gradually add water, tossing with a fork until dough forms a ball. Divide in half, making one half slightly larger.
On a lightly floured surface, roll out a larger portion of pastry to fit a 9-in. pie plate. Transfer pastry to plate; trim even with the edge of the plate. Add filling; dot with butter. Roll out remaining pastry; make a lattice crust.
Trim, seal, and flute edges. Brush with milk; sprinkle with sugar. Cover edges loosely with foil.
Bake at 400° for 15 minutes. Reduce heat to 350°; bake 40-50 minutes longer or until crust is golden brown and filling is bubbly. Cool on a wire rack.