Preheat the oven to 180°C (356°F).
Put the butter and peanut butter in a bowl and mix until smooth.
Add the sugar and combine well.
Add the egg and mix.
Sift in cake flour, baking powder, and salt, then mix together.
Shape the dough into balls and place them on a baking tray.
Press the tops of the cookies with a fork to make a pattern.
Bake in the preheated oven at 180°C for 10–12 minutes.
Let cool before serving.