Take out the margarine and wait until it is soft.
Start the oven at 175 degrees Celsius.
Mix the margarine and the sugar with a fork.
Add the vanilla sugar and egg yellow and mix it together.
Add the potato flour and make a firm dough.
Place a baking paper on a baking sheet.
Make small balls of the dough and place them on the baking paper.
Make a small hole in the middle of the cookies, and cover it with jam.
Place the cookies in the middle of the oven for approx twenty minutes.
Take out the cookies and let them cool down in room temperature.