Preheat the oven to 180°C (356°F).
Wash the yuja jam thoroughly, remove the peel and seeds, then finely chop it.
In a bowl, mix cake flour, baking powder, sugar, and salt.
Add cold butter and crumble it with your hands.
Add the chopped yuja jam and milk, and gently knead into a dough.
Roll the dough out to 2cm thick and shape into triangles or circles.
Place on a baking sheet and bake at 180°C (356°F) for 20–25 minutes.
Let cool before serving.