In a microwave-safe bowl, combine the butter, cocoa, brown sugar and milk. Microwave until mixture boils, about 3 minutes. Stir in powdered sugar and vanilla.
Pour into a greased 8 -inch square baking pan. In another microwave-safe bowl, heat caramels and water for 2 minutes, or until melted Stir in peanuts; spread over chocolate layer. Microwave chocolate chips for 1 minute, or until melted; spread over caramel layer. Chill until firm.