Preheat oven to 350° F.
Place flour, butter, powdered sugar and walnuts in blender. Blend until mixture becomes coarse crumbs. (alternatively you can place ingredients in a bowl and mix with pastry cutter)
Press mixture into greased 9X13 baking pan. Bake for 10-13 minutes. Do not brown.
Remove from oven and let cool.
Place pudding mix, buttermilk and pie filling in large bowl. Beat with a mixer until well incorporated.
Spread over crust and refrigerate until ready to serve.