Peel, core, and cut apples. In a large bowl mix together apples (and optional blackberries), sugar, instant tapioca, cinnamon, and nutmeg. Let stand 15 minutes to allow juices to thicken. While filling stands to thicken, make cookie crust.
Cream together butter and sugar. Add egg, vanilla, and milk and beat well. Sift together flour and salt and add to creamed mixture. Stir until dough comes away from the sides of the bowl and forms a ball. Set dough aside.
Whisk together or beat with a fork, the egg and cream to make the pastry wash.
Place pie shell on baking sheet.
Roll out sweet cookie crust ¼ inch thick and cut with a decorative cutter. (My favorite is a 2-inch scalloped round biscuit/cookie cutter)
Spoon apple filling into bottom crust pressing well into the pan. Mound apples in the center and taper to the sides of the pan.
Starting at the pie’s edge, arrange cookies on top of apples decoratively. Scraps can be rerolled and cut as needed.
Brush cookie crust with pastry wash and sprinkle generously with decorative white sugar.
Cover pie completely with a tent of aluminum foil.
Bake pie 55 minutes. Remove aluminum tent and continue to bake an additional 12 to 15 minutes until crust is golden brown. Remove pie from oven and cool on a wire rack.