Preheat oven to 175° C / 350° F + grease the pan with butter

Combine melted butter, oil and sugars together in a medium-sized bowl. Whisk well to combine. Add the eggs and vanilla; beat until lighter in colour (another minute).

Sift in flour, cocoa powder and salt. Gently fold the dry ingredients into the wet ingredients until JUST combined (do NOT over beat as doing so well affect the texture of your brownies).

Bake for 18-20 mins