Preheat oven to 350°. Grease a 9″x 13″x 2″ baking pan.
Combine cake mix, melted butter, and 1/3 cup of evaporated milk in a large bowl. Using an electric mixer on medium speed, beat until smooth. Spread half of the dough in baking pan. Set aside remainder of dough.
In a large saucepan, combine caramels and 1/3 cup evaporated milk. Cook, stirring constantly, over medium-low heat until melted and smooth. Pour evenly over dough in pan. Sprinkle with nuts and chocolate chips. Drop remaining dough over the nuts and chocolate.
Bake for 20-25 minutes. Cool in pan on a wire rack.
Makes 48 bars, which can be stored in an airtight container at room temperature for 3 days or frozen for 3 months.