Preheat oven to 350°. Coat a 9″x 13″ baking pan with cooking spray. Set aside.
Using an electric mixer, combine flour, brown sugar, peanut butter, and butter. Remove 1 cup of mixture and set aside.
Mix in baking powder and baking soda. Mix in milk and vanilla. Add eggs, 1 at a time, mixing well after each addition.
Transfer batter to prepared pan. Sprinkle top with reserved flour mixture and chocolate chips. Bake 35-40 minutes, or until a toothpick inserted into the center comes out clean.