Wash yak-kong (black soybeans) thoroughly and boil, then let cool.
Finely grind the boiled yak-kong and set aside.
In a bowl, cream together butter and sugar.
Add the egg and mix well.
Sift in the finely ground yak-kong, cake flour, almond flour, and baking powder.
Mix the ingredients evenly to make the dough.
Shape the dough into rounds and place them on a baking pan.
Bake in a preheated oven at 180°C (356°F) for 15 minutes.