Grind the oatmeal finely to use as a flour substitute.
Cream the butter and sugar together in a bowl.
Add the eggs one at a time, mixing well after each addition.
Sift in the oat flour, baking powder, and salt, and combine the mixture.
Pour in the milk to make a smooth batter.
Pour the batter into a pound cake mold.
Bake in a preheated oven at 180°C (356°F) for 40 minutes.
Transfer to a wire rack and let it cool completely.