Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 9x13 inch pan.
Prepare pudding as directed on box. Allow to cool slightly. Mix in yellow cake mix. Stir well. Pour batter into 9x13 cake pan. Sprinkle top with butterscotch chips and chopped walnuts.
Bake in preheated oven for 35 to 40 minutes. Cut into squares and serve.