Preheat the oven to 350°F and grease and line a 12×8 baking pan with parchment paper.
In a large bowl, mix melted butter, oil, granulated and brown sugar until well combined.
Add vanilla and eggs, beat for 30 seconds until the batter lightens in color.
Sift in flour, cocoa powder, and salt. Mix lightly until just combined.
Gently fold in the chocolate chips.
Pour the batter into the prepared pan and spread evenly.
Bake for 25–30 minutes until the center no longer jiggles. Adjust baking time for your preferred brownie texture.
Remove from the oven and let cool completely before frosting.