Step 1
Preheat oven to 175C (350F).
Step 2
Grease an 8 x 12-inch baking pan or line with baking paper.
Step 3
Combine melted butter, oil and sugar together in a bowl. Whisk well to combine. Add the eggs and vanilla and beat until lighter in colour.
Step 4
Sift in flour, cocoa powder, and salt. Fold the dry ingredients into the wet ingredients until just combined.
Step 5
Fold in ¾ of the chocolate chips. Pour batter into prepared tin, smoothing out the top evenly and topping with the remaining chocolate chips
Step 6
Bake for 20-25 minutes