Preheat oven to 350°. In a large bowl, beat the sugar, cocoa, oil, eggs and milk. Combine the flour, salt and baking powder; gradually add to egg mixture until well blended. Fold in chocolate chips and 1/2 cup walnuts. , Spoon two-thirds of the batter into a greased 13x9-in. baking pan. Bake for 12 minutes., Meanwhile, in a large saucepan, heat the caramels and condensed milk over low heat until caramels are melted. Pour over baked brownie layer. Sprinkle with remaining walnuts., Drop remaining batter by teaspoonfuls over caramel layer; carefully swirl brownie batter with a knife. , Bake until a toothpick inserted in center comes out with moist crumbs (do not overbake), 35-40 minutes more. Cool on a wire rack.