Slit open the vanilla sticks, coarsely grind 4 sticks and put them together with all the other ingredients in a sealable bottle, shake well and leave to stand in a cool place for at least 6 weeks. Shake every day to dissolve the brown sugar.
Filter the liqueur and add the vanilla sticks again, let stand for another 2 weeks, so it ripens.
The brown sugar also gives it a brown color, if you don`t like this, you can also use normal white sugar!