Preheat oven to 350 °F. In a large mixing bowl, combine cake mix and nuts if desired. Stir in butter and 2/3 cup evaporated milk; mix well. Press 1/2 of cake mixture into bottom of an ungreased 13 x 9 inch backing pan. Bake for 15 minutes. Melt caramels with 1/3 cup milk over low heat stirring until smooth. Sprinkle chocolate chips over brownie, drizzle with caramel mixture. Drop remaining cake mixture by heaping teaspoon over caramel mixture. Bake for 25 to 30 minutes or until center is set. Cool in pan on wire rack.