Pre-heat the oven to 150°C (300ºF).
Line a large baking tray with baking paper.
Beat the butter, sugar and vanilla until it is smooth and fluffy.
Add the oil a little at a time, just until incorporated.
Mix the hjorthornssalt with a little of the flour and add to the oil/butter mixture.
Add the remaining flour and mix well.
Divide the dough into around 15-20 small pieces of similar size/weight.
Roll them into balls and place on the baking tray with a little space in between them.
Bake for around 15-20 minutes, just until the edges are starting to brown a little. The cookies will be very pale, but that's how they are supposed to look.
Remove from the oven and allow the cookies to cool for about 15 minutes before moving to a wire rack. Do this with great care, as the cookies will be very delicate.