Make the crust: Combine flour and salt. Cut in butter and shortening until mixture resembles coarse crumbs. Gradually add ice water, mixing until dough just comes together.
Press half of the dough into a greased 9x13 inch baking pan.
In a bowl, combine apples, sugars, cinnamon, nutmeg, allspice, and flour.
Spread apple mixture over the crust.
Roll out the remaining dough and place it over the apple filling.
Bake for 30-35 minutes, or until crust is golden brown and filling is bubbly.
Let cool completely before cutting into bars.
Notes
These bars are best served warm with a scoop of vanilla ice cream.