Combine oatmeal, flour, and baking powder in a bowl and mix.
Cream the butter and sugar together until smooth.
Add the egg and mix thoroughly.
Combine the dry and wet ingredients.
Add chopped nuts and raisins to the dough and mix evenly.
Shape the dough into rounds and place them on a baking sheet.
Bake in a 180°C oven for 12-15 minutes.
Transfer the cookies to a cooling rack to cool.