Preheat the oven to 180°C (356°F).
Soften the butter and peanut butter until smooth.
Add the sugar and mix well.
Add the egg and combine thoroughly.
Sift in cake flour and baking powder, then mix until just combined.
Shape the cookie dough into balls and place them on a baking tray.
Use a fork to make a crisscross pattern on each cookie.
Bake in the preheated oven for 12-15 minutes.
Transfer to a cooling rack and let cool.