Pastry: Lightly grease a 9-inch pie pan. Process the flour, salt, and butter in a food processor until the mix resembles fine crumbs. Add confectioner's sugar and blend. Combine water and egg yolk in a small bowl and gradullay add to the flour mixture until it comes together as a dough. Transfer to a lightly floured work surface and shape into two (2) disks. Cover with plastic wrap (cling film), and refrigerate for 1 hour. Roll the pastry disks out on a lightly floured work surface to 1/4 inch thick. Line the prepared pan with one of the disks, leaving any excess pastry hanging over the edge. Place the other disk on a plate a refrigerate both for 30 minutes. Preheat oven to 400 F.
Filling: Peel, core, and slice the apples into a medium bowl. Add the Black Currants, sugar, flour, cinnamon, and lemon zest and toss to coat. Spoon the filling into the prepared pie pan and dot with butter. Lay the remaining pastry disk on top, pinch the edges to seal. Trim off any excess pastry. Create leaves and Black Currants out of the remaning pastry to decorate the top. Beat the egg yolk and milk in a small bowl and brush over the pastry. Cut a few slits in the pastry using a small knife to allow steam to escape during baking.
Bake for 40 - 45 minutes, or until pastry is golden brown and the filling is cooked. Serve warm.