In a microwave-safe bowl, combine butter, cocoa powder, brown sugar and milk. Microwave until mixture boils. Stir in confectioners' sugar and vanilla extract. Pour into prepared pan.
In a microwave-safe bowl, microwave caramels and water until caramels melt. Stir in peanuts. Spread mixture over chocolate layer.
In a small microwave-safe bowl, combine semisweet and milk chocolate chips; microwave until melted. Spread over caramel layer. Chill for 2 hours, or until firm.