Whisk the flour and salt for the crust together. Cut in the cold butter until coarse crumbs form with some pea-sized pieces remaining, then gradually toss in the ice water until the dough just comes together.

Shape the dough into a disk, wrap it, and chill for at least 30 minutes. Roll it into an approximately 12-inch round, fit it into a 9-inch pie plate, trim and crimp the edge, and chill the crust while preparing the filling.

Combine the sliced apples, cranberries, currants, sugar, flour, cinnamon, and salt. Toss gently until evenly coated, then transfer the fruit to the chilled crust.

Combine the crumb-topping flour and brown sugar. Cut in the cold butter until coarse crumbs form, then mix in the chopped walnuts or pecans and scatter the topping over the fruit.

Place the pie on a baking sheet and bake at 375°F for 20 minutes. Reduce the oven to 350°F and bake for approximately 45–55 minutes more, until the topping is browned and the fruit bubbles around the edges.

Cool the pie for at least 2–3 hours before slicing. This resting time allows the juices to thicken and the crumb topping to firm up.