Crush the mastic tears into the mortar, adding 1 tsp sugar.
In a big bowl sift flour and whisk it together with baking powder, mahleb and grated mastic.
Beat butter, sugar and vanilla extract, using an electric mixer, until light and creamy.
Add eggs, one at a time then orange zest, beating in a lower speed until incorporated.
Add baking soda to the orange juice to froth and then add mixture into the bowl with the wet ingredients.
Add 3-4 tbsp flour into the wet mixture and combine softly.
Then you put everything in the bowl with the flour and you knead with hands gently until all ingredients are well incorporated into a fine, buttery dough. Don’t over knead the dough because it can harden.
Even if you think the dough is sticky, don’t add extra flour.
Cover it with a towel and let it rest for 15-20 minutes.
Preheat the oven to 180o Celsius.
Line two large cookie sheets with parchment paper and shape cookies.
Don’t forget to brush with the egg wash for a shiny color.
Bake for 16-18 minutes until nice and golden.
Let them sit onto a cooling rack to cool completely ant then store them into an airtight container.
Butter and eggs should be at least two hours out of the fridge.