Apple Pie Crust: Mix the flour, salt and Clabber Girl Baking Powder in a large bowl. Add the butter. Using a pastry blender or your fingers, cut the butter into the flour until the mixture resembles coarse bread crumbs with some pea-size pieces of butter. Gradually stir in enough of the water for the dough to clump together. Gather up the dough and form into a disc, wrap in plastic wrap, and refrigerate until chilled but not hard, 1 to 2 hours.
On a lightly floured work surface, roll out the dough into a 1/8-inch-thick round. Transfer to a 10-inch pie dish, trimming the dough to a 1/2-inch overhang around the edges of the dish. Tuck the overhang under the dough on the rim and flute the edges. Prick holes in the bottom with a fork. You can make the crust in advance and store in the freezer for up to 3 days. No need to thaw the crust before baking.
Apple Walnut Pie Filling: Melt the butter in a wide skillet over medium low heat, stirring in the sugar and spices. Add the apple slices and lemon zest, stirring to coat evenly. The mixture should be bubbly but not hot enough to crystallize or brown the sugar. Continue cooking and stirring for 5-6 minutes. Remove from the heat and cool the apples in a separate shallow bowl.
Apple Pie Streusel: Combine the oats, flour, walnuts, brown sugar and salt in a bowl. Add the butter and blend together with your fingertips until the mixture is crumbly.
To Bake: Set a rack in the center and pre-heat the oven to 375 degrees F. Spread the apples evenly in the crust and sprinkle the streusel evenly over the top. Bake for 12 minutes and, without opening the door, reduce the heat to 350 degrees F. Bake for another 35 - 45 minutes, checking after 30 minutes. Cool briefly and serve.
Recipe submitted by Mani Niall.