Preheat oven to 340 degrees F (170 deg C).
Separate Egg (4) yolks from the whites and set both aside.
Beat the Salted Butter (250 gram), Caster Sugar (100 gram) and Vanilla Extract (1/2 teaspoon) till light and creamy. Add in the egg yolks one at a time, until mixture incorporated, mix well.
On low speed, fold in the Self-Rising Flour (200 gram), alternating with the Milk (60 milliliter). Mix till well incorporated. Then divide the batter into two portions, adding the Matcha Powder (1 tablespoon) into one portion and mix well.
For meringue, in a clean bowl, whisk egg whites until foamy at low speed and gradually in the Caster Sugar (50 gram) and beat from medium to high speed till stiff peaks. Fold half of the meringue into the plain and matcha batter in two batches till just combined with a rubber spatula.
Spoon a layer of plain batter into the pan and level it. Sift a thin layer of Unsweetened Cocoa Powder (to taste) on top until evenly covered, very gently dollop a layer of matcha batter on top of the cocoa powder. Just to be patient in doing this step. Repeat with the remaining layer, do not dust cocoa powder on the top layer.
Bake for 45-50 minutes or until skewer inserted into cake comes out clean.
Leave cake to cool in pan for 15 minutes. Then remove cake and place on wire rack to cool. Serve and enjoy!