Preheat the oven to 200°C (392°F).
In a bowl, mix cake flour, baking powder, sugar, and salt.
Cut in cold butter and mix with your fingertips until it resembles coarse crumbs.
Mix milk and egg together, and add about 80% of it to the dry ingredients, then knead into a dough.
Once the dough comes together, place it on a baking sheet and roll it out to about 2–3 cm thick.
Cut out rounds with a cutter or slice into triangles.
Line a baking pan with parchment paper and place the dough pieces on top.
Brush the tops with the remaining milk and egg mixture.
Bake in the preheated oven for 15–20 minutes.