Preheat the oven to 325˚F. Prepare the pan by spraying it with cooking spray and lining it with two pieces of parchment paper to create a sling. Then, spray the parchment paper with cooking spray and set the pan aside.

Stir together the granulated sugar, brown sugar, melted butter, vegetable oil, and vanilla extract with a wooden spoon.

Using a wooden spoon, mix in the eggs one at a time.

Sift cocoa powder, flour, baking powder, and salt into the wet ingredients. Stir until just combined.

Fold in the semi-sweet and milk chocolate chips.

Spread in a greased, parchment-lined 8x8 pan.

Bake at 325˚F for 50-55 minutes or until a toothpick inserted in the center comes out with some crumbs attached. Place pan on a wire rack to cool. Use the parchment sling to lift the brownies from the pan and cut into squares using a plastic or nylon knife.