Place the butter in the bowl and whisk together with the sugar at low medium speed, until creamy, 1-2 minutes.
Add the egg and vanilla, beat until mixed. Reduce speed and dry ingredients in three additions and chopped chocolate.
Separate the dough in half and shape each half of elongated sausages. Cover with film and press both ends with the hand towards the center to tighten the dough. Chill prepared dough for at least 3 hours.
Remove the cold dough and cut the cookies to a thickness of 1 centimeter. Place each cookie a couple of centimeters away on a baking sheet. Bake until the biscuits are lightly browned, about 18-20 minutes. Transfer the cookies to a grid to cool completely.