Preheat oven to 350. Grease 8×13” pan and set aside. In a large mixing bowl, combine the melted butter, sugar, flour, eggs, milk baking powder, sifted cocoa powder and vanilla. Stir until just moistened. Pour into the pan and bake for 40 minutes or until toothpick comes out clean. Sprinkle the chocolate chips over the top of the warm brownies. Wait until the chips are partially melted, 3 to 5 minutes, and then use a flexible spatula to gently spread evenly over the brownies.