1. In a small bowl, combine brandy and currants. Cover and let stand until currants are plump, at least 1 hour or up to 1 day.
2. Preheat oven to 375°. Sort cranberries and discard any that are bruised or decayed. Rinse and drain berries.
3. In a large bowl, mix 1 1/4 cups granulated sugar, 6 tablespoons flour, orange zest, cinnamon, nutmeg, and salt. With a slotted spoon, lift currants from brandy; reserve brandy. Add currants, cranberries, and apples to sugar mixture and mix well. Taste and add more granulated sugar if desired. Pour filling into unbaked 10-inch pie pastry in pan. Drizzle evenly with reserved brandy.
4. In another bowl, mix 1 cup flour and the brown sugar. Add butter and cut in with a pastry blender or rub with your fingers until mixture forms small lumps. Sprinkle topping evenly over filling. Set pie in a foil-lined 12-inch pizza pan or 10- by 15-inch baking pan.
5. Bake on the bottom rack until juices bubble around edges and through topping, 55 to 65 minutes. If pie browns too quickly (check after 30 minutes), cover loosely with foil.
6. Set pie, uncovered, on a rack until cool to touch, 2 1/2 to 3 hours. Cut into wedges.
If making it up to 1 day ahead, cover and chill. To warm the cold pie, bake uncovered in a 350° oven 10 to 15 minutes.