8-10 large Granny Smith apples, peeled, cored, and thinly sliced. Using a pastry blender or 2 knives, cut the butter into the flour mixture until coarse crumbs form. Bring to a boil over medium-low heat, stirring. Return pan to the heat. Cook , stirring, for 1 minute. remove pan from heat.
Place apples slices in a large bowl.
Stir in the filling mixture until well combined. Place oven rack in the lowest position. Spoon filling into crust. Roll the remaining dough into an 11-inch circle. Moisten rim of the bottom crust water , then cover filling with top crust.