Preheat oven to 340 degrees F (170 degrees C). Line a 23x13cm loaf pan with parchment paper
Sift Cake Flour (150 gram), Baking Powder (1/4 teaspoon), and Matcha Powder (1 tablespoon) together and set aside.
Beat Unsalted Butter (150 gram) and Powdered Confectioners Sugar (130 gram) together with a handheld electric mixer till light and fluffy, takes about 8 minutes. Gradually add Egg (3) and beat well.
Sift in flour mixture the second time into egg mixture in 2 portions and fold through completely with a rubber spatula.
Pour half of the batter into prepared loaf pan and spread some Red Bean Paste (to taste) over it. Then top up with the remaining batter and smooth evenly with a rubber spatula.
Bake in the preheated oven for about 40 minutes or a skewer into the center of the cake comes out clean.
Remove the cake in loaf pan after baked, then cool the cake completely on wire rack. Lastly dust some matcha powder over the cake before slicing. Serve and enjoy!