Preheat oven to 180 degrees C (350 degrees F).
In a mixing bowl, sift All-Purpose Flour (1/3 cup), Baking Powder (1/4 teaspoon)
In another bowl, whisk Egg (2) and Vanilla Essence (1 teaspoon) till light and fluffy
As you beat the egg, add Caster Sugar (1 cup) a little at a time till half is done and add the balance nd incorporate fully.
Add flour and flod in.
Add Unsalted Butter (1/2 cup) and Unsweetened Cocoa Powder (1/2 cup) into the mixture.
Add the Walnut (1/2 cup) and mix.
Prepare tin by brushing with melted butter.
Pour the batter into a prepared rectangle tin.
Bake for 25 to 30 minutes. Check if cooked by using a toothpick. Cut into squares. Serve and enjoy!