Preheat oven to 350 degrees. In a bowl, combine butter and cake mix. Stir in 2/3 cup evaporated milk. Spread 1/2 chocolate batter into greased 13x9 pan. Bake for 15 minutes. Meanwhile, melt together caramels and remaining milk. Spread chocolate chips over baked chocolate mix, then drizzle caramel mixture, then drop remaining chocolate batter by spoonfuls over caramel mixture. Bake for an additional 20-25 minutes. Cool completely before serving.