In a bowl, stir together the first five ingredients listed. Butter a square baking dish and press the peanut butter batter into the pan.
In a microwave safe bowl, combine the chocolate chips and oil. Melt on high for 30 seconds, stir, then melt for another 30 seconds. If needed you can melt it for an additional 15-30 seconds.
Pour the melted chocolate over the top and spread to the edges of the pan. Sprinkle on the chopped peanut butter cups.
Cover and freeze for 30 minutes to an hour (or overnight). Once hardened, cut into squares. You can serve these right away or wrap each bar and store in the freezer.