Preheat the oven to 200°C (392°F).
Combine cake flour, baking powder, sugar, and salt in a bowl.
Cut cold butter into small pieces and rub it in with your fingertips until the mixture becomes crumbly.
Add the egg and milk, and bring the dough together into one ball.
Roll the dough out to a thickness of 2cm and cut into rounds.
Place the rounds on a baking sheet and brush with beaten egg.
Bake in the oven for 15–18 minutes until golden brown.