Soften the butter by bringing it to room temperature. Combine it with the shortening. Add the sugar and mix well.
Add the egg and continue mixing.
Add a little few drops of vanilla extract and mix well.
Add the flour and baking powder. Switch to a rubber spatula and briskly fold into the dough.
Mix in the oatmeal.
The consistency should resemble hamburger patties. Form into small round balls and place on a parchment-paper-lined baking sheet.
Use your fingers to press down on the cookies to flatten. They will spread when baking, so leave some space between each one.
Sprinkle the tops with brown granulated sugar and salt.
Bake in a preheated 180C oven for 15-20 minutes and they're done.