Blend together the flour, margarine and chopped nuts and press into a 9 x 13 inch pan. Bake for 15 minutes at 350° F. Cool. Cream together powdered sugar and cream cheese; then fold in 9 ounce defrosted cool whip. Spread onto the cooled pastry layer. Mix together the instant pudding and milk; spread on top of second layer. Spread a 9 ounce container of defrosted cool whip on top of third layer. Refrigerate.