Preheat the oven to 350°F. Line an 8x8-inch nonstick baking dish with parchment paper and set it aside.
In a heat-safe small bowl, add the chocolate chips and the oil. Microwave for 45 seconds. Stir the chips and oil, return to the microwave, and heat for another 10 seconds. Stir until the chips and oil are smooth. Set it aside.
Using a medium-sized mixing bowl whisk together all-purpose flour, granulated sugar, baking soda, and salt. Set it aside.
In a small bowl, whisk together the eggs, vanilla extract, and milk. Add to the flour mixture. Now add the melted chips and stir until the batter is just combined.
Toss the chopped peanut butter cups with 1 tablespoon of flour. Fold the coated chopped peanut butter cups into the batter and mix just until all ingredients are combined.
Pour the batter into the prepared baking dish.
Using a 1 to 1½ tablespoon cookie scoop or a regular tablespoon, dollop the peanut butter on top of the brownie batter. Use a knife to swirl the peanut butter.
Bake for 30 minutes.
Allow the brownies to cool completely before cutting.