Make the pastry dough: In a large bowl with a pastry blender or in a food processor blend or pulse together flour, sugar, salt, and butter until mixture resembles coarse meal. Add 2 tablespoons ice water and toss with a fork or pulse until incorporated. Add enough remaining ice water, 1 tablespoon at a time, tossing or pulsing to incorporate, until mixture begins to form a dough. On a work surface smear dough in 3 or 4 forward motions with heel of hand to slightly develop gluten in flour and make dough easier to work with. Form dough into a ball and flatten to form a 1-inch-thick disk. Wrap dough in plastic wrap and chill 30 minutes.
Make the topping: In a small bowl with your fingertips blend butter, brown sugar, and flour until smooth and blend in nuts. Chill topping, covered.
Make the filling: Peel and core apples. Cut apples into 1/2-inch wedges and in a bowl toss with remaining filling ingredients to coat.
Preheat oven to 350 degrees.
On a lightly floured surface roll out dough into a 15-inch round (about 1/8-inch thick) and fold into quarters for ease of handling. Unfold dough in a well-seasoned 10-inch cast-iron skillet or 10-inch deep-dish (1 1/2-quart) pie plate, easing to fit and letting dough overhang rim of skillet or pie plate. Spoon filling into shell and fold pastry overhang over filling, leaving center uncovered. Bake pie in middle of oven for 1 hour (pie will not be completely cooked) and remove from oven.
Crumble topping over center of pie, breaking up any large chunks. Brush crust with milk and sprinkle with sugar. Bake pie in middle of oven 30 minutes more, or until crust is golden and filling is bubbling. Cool pie on a rack. Serve pie warm or at room temperature with ice cream.