Remove the butter from the refrigerator in advance and sift the flour through a sieve.
Mash the butter in a deep bowl, add sugar to it and beat everything with a mixer. Add eggs to the mixture and continue beating until smooth. Add oatmeal and flour to the mixture and mix thoroughly.
Line a baking tray with baking paper. Using a spoon, place the dough onto the paper in medium balls spaced apart. Place the cookies in the oven and bake at 180°C for no more than 15 minutes.
Serve oatmeal cookies with a cup of tea or coffee.