1. Melt butter in a medium saucepan over medium heat. Stir in brown sugar and milk. Bring to a boil and boil for 2 minutes, stirring frequently. Remove from heat. Stir in peanut butter and vanilla. Pour over confectioners' sugar in a large mixing bowl. Beat until smooth; pour into an 8x8 inch dish. Chill until firm and cut into squares.
