Mix cake mix, butter, 1/3 cup milk. Spread 1/2 of cake mixture into a 9′x13′ greased pan. Bake 6 minutes at 350 degrees. Melt caramels and 2/3 cup evaporated milk in a double boiler until smooth. Remove cake from oven. Sprinkle chocolate chips on top, then nuts, and finally pour caramel mixture over all. Spread the remaining cake mixture over the caramels evenly. Bake 20 minutes at 350 degrees.