Cream the butter and sugar together until light and fluffy.
Add tahini and mix well.
Add the egg and mix again.
In another bowl mix flour, cocoa, baking powder and sesame seeds.
Mix the dry ingredients with the wet ingredients until the dough comes together.
Shape the dough into a disc, cover with plastic wrap and let sit in the fridge for at least one hour or overnight. At this point, you may even freeze it for later.
Roll the dough and cut into shapes using a cookie cutter.
Preheat the oven for at least 10 minutes before baking at 180 degrees Celsius.
Bake in the preheated oven for around 8-10 minutes.
Let them cool in the pan for 10 minutes before moving to a wire rack to cool completely.
Keep in an airtight container at room temperature for up to 2 weeks.