In a small bowl, mix together the peanut butter and 3 tablespoons of sugar. Set aside.
In another bowl, melt the 1 cup of chocolate chunks. Do this in 30 second intervals in the microwave, stirring the chocolate chunks every 30 seconds until melted.
In a mixing bowl, whisk together all of the dry ingredients, from the flour to the baking powder. Add in the oil, milk, and melted chocolate and stir until combined.
Pour the brownie batter into your lined baking dish.
Spoon the peanut butter mixture onto the brownie batter in stripes or blobs and run a knife back and forth through both mixtures to form a swirl.
Bake the brownies for about 30-35 minutes or until your desired doneness.