Preheat oven to 350 degrees. In a mixing bowl, combine flour, cocoa, baking powder and salt. Set aside. In a medium sized mixing bowl combine the melted butter and brown sugar and sugar. Mix until combined. Add the eggs and vanilla. Then add the dry ingredients and mix well until incorporated.
Spread in a greased 9x13 inch pan. I always line my pan with aluminum foil and spray with cooking spray so that they can life out easily. Bake for 30-35 minutes or until toothpick inserted in center comes clean. Let cool completely before frosting.
To make the cookie dough frosting: Beat together the softened butter and sugar. Add in the vanilla until mixed well. Add flour and salt. Stir in the milk and beat until the frosting is fluffy. Stir in the chocolate chips. Spread the frosting carefully on cooled brownies.