Preheat oven to 350 ℉. Lightly grease an 8x8" metal baking pan with nonstick cooking spray, line with parchment paper, then lightly grease the parchment as well. Set aside
In a mixing bowl, combine the melted butter and sugar and stir to help the sugar dissolve. Add the vanilla extract, eggs, oil, and melted chocolate and mix until combined.
Sift in the flour, cocoa powder, baking soda, and salt, and gently fold in until no raw flour is visible. Gently fold in the chocolate chips.
Pour the batter to the prepared baking pan. Bake for 40-45 minutes, until a toothpick inserted in the center comes out with a few wet crumbs. Allow the brownies to fully cool in the pan on a wire cooling rack before cutting into slices.