Soften the butter.
Add sugar and salt, and cream together.
Add the egg and mix well.
Sift cake flour, cocoa powder, baking powder, and salt, then add to the mixture.
Add Oreo cookie pieces and knead the dough.
Pinch off small pieces, shape into balls, and place on the baking sheet.
Bake for 12 minutes in a preheated oven at 180°C.