Combine 1/4 cup butter, 1/4 cup milk, cream cheese and chocolate chips in 2-quart saucepan. Cook over medium heat, stirring occasionally, 6-8 minutes or until melted. Remove from heat. Stir in powdered sugar and vanilla until smooth. Stir in marshmallows and peanuts. Immediately spread over hot brownies. Cool completely. Cut into bars. Store refrigerated.