Preheat your oven to 350°F (175°C).
Grease your 9x13-inch baking pan with non-stick spray or line it with parchment paper.
In a mixing bowl, combine the brownie mix, softened butter, and egg. Stir until well combined.
Pour the brownie batter into the prepared baking pan and spread it evenly.
Sprinkle the chopped Reese’s Peanut Butter Cups evenly over the brownie layer.
Sprinkle the peanut butter chips and milk chocolate chips over the top.
Pour the sweetened condensed milk over the entire mixture.
Bake for 25-30 minutes, or until the edges are set and the center is slightly gooey.
Allow to cool in the pan for about 10-15 minutes before transferring to a wire rack to cool completely.
