Soften the butter at room temperature and whisk it until smooth. Add powdered sugar and mix well.

Add one egg yolk to the butter mixture and mix thoroughly.

Divide the butter mixture evenly into two portions. For the vanilla dough, mix in 100g cake flour and 1/4 tsp baking powder. For the matcha dough, mix in 100g cake flour, 1/4 tsp baking powder, and matcha syrup.

Combine portions of the two doughs to create a marbled effect. Shape into a cylinder, wrap in plastic wrap, and freeze until firm.

Slice the frozen dough into 0.7cm thick rounds and place them on a baking sheet.