Pre-heat the oven at gas mark 4 or 350 F or 177 C.
Line your 8 inch square baking dish with baking paper. Leave the extra edges of baking paper hanging on the two sides.
In a bowl, take white sugar, brown sugar, and oil. Mix together with the help of a whisk.
Add eggs and whisk again until smooth. No over-mixing!
Place a sieve over the mixing bowl. Sieve cocoa and flour right in the bowl.
Mix wet and dry ingredients with a spatula just until combined. Scrap the sides of the bowl with rubber spatula as needed. Again do not over-mix. This mixture might be thick but that's ok.
Check after 20 minutes by shaking the dish lightly.For the moist fudgy brownie: If the batter giggles, continue to bake. If the batter is set remove it from the oven and the brownie will continue to bake in the dish. The brownie will as it cools.For a well-set fudge brownie: Once the brownie is set, check by inserting a toothpick. If you see wet crumbs, the brownie is ready. If the liquid batter is visible on the stick, bake the brownie for another 5-7 minutes.
Let the brownie cool naturally for at least 30 minutes or preferably until completely cool. Slide a knife around the edge to loosen the brownie. Then lift it out with the help of butter paper handles. Cut brownie into 16 pieces and serve.
After cooling store on the counter for 5 days or in the fridge for 10 days. You can freeze brownies for 3 months.