Dissolve yeast in lukewarm water, stirring well. Beat the eggs and sugar in the mixer until they whiten and soften well. Melt the butter at moderate temperature (be careful not burn the butter).
In a large bowl, put the flour, mastic, mahleb and zest from the oranges. Add the butter, egg and sugar mixture, milk and yeast and mix up well.
When the dough is softened and has a soft texture, cover it with a plastic film and let it rest for about 2 hours to double its volume.
Add some flour on your bench. Once the dough is ready, divide it into 6 equal parts and begin to “work”/ roll it up until it is 2cm thick.
Place baking paper in a pan. Use 3 dough sticks for each tsoureki, shape it and place each one in its own pan. Do not place them in the same pan because they will get more volume while baking and we do not want them to stick.
Let the brioches rest for half an hour at room temperature. Then, smear with egg, sprinkle with almond and bake in preheated oven at 180 degrees for 30-40 minutes.