This is sooooo good!!! But it is soooo rich, so make sure you have tall glass of ice cold milk to wash it down.
Bake brownies according to package directions. Allow them to cool in the pan. Do not cut.
In a medium saucepan over low heat, melt peanut butter chips and butter together, stirring frequently until smooth. Remove from heat and stir in the sweetened condensed milk. Spread evenly over the cooled brownies. Chill until set and cut into squares.