Chop the peanuts finely.
In a bowl, cream together the butter and sugar.
Add the egg and mix well.
Sift in the flour and baking powder, then mix together.
Add the chopped peanuts and knead the dough.
Shape the dough into small balls and place them on a baking tray.
Bake in a preheated oven at 180°C (356°F) for 15 minutes.