In micro-safe bowl, combine butter, cocoa, brown sugar and milk. Microwave on high until mixture boils, about 3 minutes. Stir in powdered sugar and vanilla. Pour into a greased 8-inch pan. In another micro-safe bowl melt caramels with water for 2 minutes, or until melted. Stir in peanuts; spread on chocolate layer. Microwave semi-sweet and milk chocolate till melted and pour over caramel layer. Chill until firm.