In a microwave-safe bowl, combine the butter, cocoa, brown sugar and milk. Microwave on high until mixture boils, about 2 minutes. Stir in confectioners' sugar and vanilla. Pour into a greased 8-in. square dish.
In another microwave-safe bowl, heat caramels and water on high for 1-1/4 minutes or until melted. Stir in peanuts; spread over chocolate layer. Microwave chocolate chips on high for 30 seconds or until melted; spread over caramel layer. Chill until firm.