Mix together the flour, walnuts, sugar and butter until crumbly. Bake for 1 hour at 275 degrees F. Mix occasionally while baking. (I use an 8x10 inch cake pan).
Beat the powdered sugar, cream cheese and Cool Whip together until light and fluffy. Spread over crust crumbs. Prepare pudding mix as for pie filling. Spread over cream cheese mixture. Top this with Cool Whip and sprinkle with chopped walnuts.
Refrigerate a couple hours or overnight before serving.