We put in a bowl the yeast and milk and mix, until yeast dissolves. Add 1 cup flour and stir to combine into a runny batter. Cover the bowl with a kitchen towel and let rest for about 30 minutes, to allow batter to rise.
In the meantime, put margarine in a small saucepan, over medium heat. When melted, stir in with a whisk the eggs, sugar, orange zest, machlepi, mastic, vanilla extract and continue stirring, until the mixture is lukewarm.
Place on the mixer the dough hook attachment.
Pour the above mixture into the mixer’s bowl. Add the egg mixture, remaining flour, salt and beat on low speed, until combined and the dough pulls apart from the sides of the bowl. If you do not have a stand mixer, you can put all the above ingredients into a bowl and knead to combine.
We place the dough into another greased bowl, cover with a kitchen towel and let the dough rise, until it doubles in size.
Grease your working surface with olive oil. Place the dough on the working surface and divide it in 6 equal pieces. Roll each piece out into strips, cover them with a kitchen towel and let them rise for about 20 minutes.
To form the "tsoureki", lay three strips side by side, pinching together at one end and braid. Pinch together at the other end to hold the loaf intact.
Place the “tsoureki” onto a baking sheet lined with parchment paper, cover them with a kitchen towel and let them rise for 30 minutes.
In the meantime preheat the oven at 300o F.
In a small bowl combine the egg wash ingredients.
Brush the "tsoureki" with the egg wash, add the almond flakes on top and bake in the preheated oven for about 45 minutes. Remove from the oven, allow to cool and then serve.