2 ½ cups flour
1 cup butter, cut into tablespoons, slightly softened
1 egg, separated, yolk slightly beaten, white reserved
½ cup milk
8 medium Granny Smith apples, peeled, thinly sliced
¾ cup sugar
2 tbsp flour
1 tbsp lemon juice
1/8 tsp ground cinnamon
1 cup confectioners' sugar
½ tsp vanilla
2 tbsp milk
Vanilla ice cream, optional
1. For the pastry, place the flour in a large bowl; add the butter. Cut the butter into the flour with a pastry blender or two forks until the mixture resembles coarse crumbs. Add the egg yolk and milk, mixing together lightly until the mixture comes together into a ball. Divide into two balls; wrap each in plastic wrap. Refrigerate 2 hours.
2. Heat the oven to 190 degrees Celsius. For the filling, toss together the apples, sugar, flour, lemon juice and cinnamon; set aside. Roll out one of the pastry balls into a rectangle a little larger than a 13-by-9-inch baking pan. Fold rectangle in half; unfold it in the pan, pressing to fit into the bottom and sides. Spoon filling over the pastry. Roll out the remaining pastry into a rectangle; fold in half. Unfold on top of the apples, tucking the top pastry over the edges of the bottom pastry. Pinch to seal; flute the edges. Set aside.
3. Beat the reserved egg white until stiff; brush it over the pastry. Bake until apples are cooked through and crust is nicely browned, about 55 minutes. Set aside to cool.
4. For topping, place confectioners' sugar in a small bowl; stir in the vanilla. Stir in the milk, a tablespoon at a time, until the mixture reaches drizzling consistency.
5. Drizzle over the top. Cut into squares; top with a scoop of vanilla ice cream, if desired.
Tip: This recipe makes enough for 20, but it keeps well for another day or two, and the pastry's crust stands up well to reheating in a 325-degree oven for 10 minutes.