Mix together flour, butter, and chopped nuts together and press into a 9" x 13" pan. Bake at 350 degrees for 20-25 minutes. Cool. Mix together cream cheese, 1/2 Cool Whip, and powdered sugar. Spread on cooled crust. Whip pudding made with 3 cups of milk instead of 4. Spread over cream cheese layer. Top with remaining Cool Whip. Chill and serve by cutting into 3" x 3" squares.