Add the flour, vanilla powder and baker's ammonia to a medium size mixing bowl and whisk to combine. (Fair warning, it smells terrible!) Set this bowl aside.
Add the butter and sugar to a large mixing bowl or the bowl of a stand mixer and cream them together until they are fully combined.
A little at a time, add the oil to the butter mixture, stirring well after each addition.
Add the flour mixture to the butter mixture and mix until fully combined.
Using a cookie scoop or a tablespoon, portion the dough out into balls, and then use your hands to roll them into smoother balls.
Arrange the cookie dough balls on your baking tray with about 2 inches (5 cm) of space in between them.
Bake cookies for about 20-24 minutes. Do not open the oven during this time, because the ammonia smell will be strong!
The cookies will be done when they no longer smell of ammonia. They should not be brown at all on top. Cool on a cooling rack.
These cookies will keep well at room temperature in an airtight container for about a week.