Mix oatmeal, flour, baking powder, and salt evenly in a bowl.
Cream the butter and sugar together, then add the egg and mix well.
Add the dry ingredients to the butter mixture and mix evenly.
Add nuts, dried fruits, etc., and knead the dough.
Shape the dough into balls and place them on a baking sheet.
Bake in a 180°C oven for 12–15 minutes.
Place on a wire rack and let them cool completely.