Cream together butter and peanut butter in a bowl.
Add sugar and mix well.
Add egg and mix.
Sift in cake flour, baking powder, and salt, then mix to complete the dough.
Shape the dough into balls, place them on a baking tray, and press them down with a fork to make a pattern.
Bake in a preheated oven at 180°C (356°F) for 12 minutes.