CRUST: Melt butter, add flour and pecans. Spread mixture in bottom of 8 1/2 x 14 inch cake pan. Make pudding by directions on box. Mix cream cheese, powdered sugar and Cool Whip until blended well. Cook crust at 350 degrees for 20 minutes. Let cool. Layer mixtures on crust. First cream cheese mixture, then chocolate pudding. Top with Cool Whip and sprinkle chopped pecans on Cool Whip (can use any flavor of pudding).