Soften the unsalted butter at room temperature and whip it with sugar until fluffy.

Gradually add eggs in portions while whipping the mixture.

Sift cake flour, baking powder, and green tea powder into the mixture.

Fold the mixture gently using a spatula until almost combined.

Add soy milk and sweet red bean paste, then mix until fully combined.

Pour the batter into a parchment-lined mold and smooth the top by lifting the edges with a spatula.

Brush oil on a knife and make a slit in the center of the batter.