Preheat oven to 350 degrees F (177 degrees C). Line an 8x8 or 9x9 baking pan with parchment paper or foil and lightly grease with cooking spray. Set aside.
In a large bowl add mix together the flour (spoon flour into measuring cup and level off with the back side of a knife for accurate measurement), cocoa powder (spoon cocoa powder into measuring cup and level off with the back of a knife for accurate measurement), chocolate chips, baking powder and salt. Mix until combined. Pour in the oil, eggs and vanilla. Pour in the melted chocolate and stir all just until combined. Don't overmix!! Spread evenly into prepared pan and bake for 40 minutes or until a toothpick inserted comes out with SOME MOIST CRUMBS. DO NOT OVERBAKE if you want moist and chewy brownies. Cool completely before cutting.