To prepare the pie crust, place flour and salt in the bowl of a food processor and pulse to combine. Or, whisk together in a medium bowl.

Add butter and shortening and pulse in the food processor or cut in using a pastry blender just until mixture resembles coarse crumbs.

Add ice water 1 tablespoon at a time, until dough just comes together.

Gather up dough, pat into a disc, cover and chill at least 30 minutes.

Meanwhile, make the topping. In a medium bowl, stir together flour, walnuts, brown sugar and salt.

Mix in butter with fingertips until mixture resembles coarse crumbs. Set aside.

When ready to bake, preheat the oven to 400°F. Roll pie dough out on a lightly floured surface into a 12-inch circle.

Place dough in 9 1/2-inch pie plate and press into place.

Trim and fold under the edges and crimp for a decorative crust. Chill in refrigerator while making the filling.

In a large bowl, whisk together sugar, flour, cinnamon, lemon zest and salt until combined.

Add apple slices and lemon juice and toss until evenly coated.

Spoon apple filling into pie shell and sprinkle evenly with crumb topping.

Bake pie on lower rack of oven 20 minutes.

Reduce oven temperature to 350°F and continue to bake 45 to 50 minutes longer or until apples are tender and topping is golden and crisp. Cool on a wire rack.