Preheat oven to 350F.
Spray a 9x13 in baking dish with cooking spray and line with parchment paper. Set aside.
Combine caramels and 1/3 cup evaporated milk in a microwave safe container. Heat on high heat in 30 second intervals, stirring in between, until fully melted. Set aside.
Combine cake mix, melted butter, 1/3 cup evaporated milk, mini chocolate chips, and chopped nuts in a bowl. Stir just until combined.
Spread half of the cake mixture onto the bottom of the baking dish and bake for 7 minutes.
Remove from the oven and sprinkle on one cup of chocolate chips. Drizzle the caramel sauce on top. (If caramel has cooled to the point that it cannot be drizzled, return to the microwave for 10 seconds and stir.)
Spread the remaining half of the cake mixture over the top of the caramel and chocolate chips. It's okay if you don't get 100% coverage. Bake for 15-18 minutes.
Serve immediately with ice cream or let cool before cutting into bars.
Store in an airtight container for up to 4 days.