Preheat your oven to 350°F (175°C). Line a 9x13 inch baking dish with aluminum foil and spray with non-stick cooking spray.

In a large mixing bowl, combine ½ cup of softened unsalted butter, one large egg, and ¼ cup of vegetable oil. Gradually add in the brownie mix and blend until a thick batter forms.

Press the mixture evenly into the prepared pan to create the brownie base.

Sprinkle the chopped Reese’s Peanut Butter Cups and peanut butter chips evenly across the brownie base.

Drizzle about ¾ of a 14 oz can of sweetened condensed milk over the toppings.

Bake for 28-30 minutes until edges are set and center has a slight jiggle.

Cool at room temperature for about 10 minutes, then refrigerate for at least an hour before slicing into squares.