In a bowl, mix the flour, baking powder, vanilla and mastic. Mix the orange zest with the sugar. In another bowl, or in the bowl of the mixer, add the butter and blend on high speed with the whisk, or with the K-beater of the mixer. Add the sugar and continue blending until they fluff up. Add the eggs one by one. Add half of the flour. Add the orange juice and the rest of the flour. Knead lightly with the hands until the dough is soft and easy to manipulate without sticking to the hands. Press it lightly and cover the bowl with cling film. Put it in the fridge for 30 minutes. Preheat the oven at 170°C and cover 2 pans with non-stick baking paper.
To shape them: Remove the dough from the fridge and work the biscuits. Take a piece of dough (30g) and shape a stick of 15cm. Bend the top edge of the stick towards the middle, and the bottom towards the middle from the other side, shaping an S. Place the biscuits in the pans. Coat with the egg and, depending on preference, sprinkle with the sesame seeds. Bake in the preheated over for 20-25 minutes or until golden-brown.