1. In a small saucepan, combine the milk, sugar, and eggs. Place over heat and whisk with a whisk until the mixture is lukewarm, about 36-40 degrees Celsius. Be careful, if the mixture gets too hot, it will 'kill' the yeast.
Place the flour, salt, mahlab, mastic, cardamom, and yeast in the mixer bowl and mix. Pour in the milk mixture and knead well.
When you reach 70% of the kneading process, add the unsalted butter, a spoonful at a time. Knead at medium speed for 20 minutes.
2. Cover the bowl with plastic wrap and set aside for 4 hours to rise. To make it rise faster, cover with a towel. Also, if you want a quicker rise, preheat the oven to 35-40°C and place the bowl (covered with plastic wrap) inside. It will have risen in 1 ½ - 2 hours. One way to check if the dough is ready is to place a small round piece of dough in a glass of water. When it floats to the surface, it is ready. Keep this glass next to the dough. If you choose to let the dough rise in the oven, place the glass inside the oven as well.
3. When the dough has risen, uncover it and fold it over (bring the edges towards the center and knead). Cover the bowl again with plastic wrap and let it rise for 1 – 1 ½ hours. Alternatively, place it covered in the oven for about 1 hour, or repeat the trick with the glass of water and the dough.
When the dough has risen, take it out of the bowl and cut it into 3 pieces. Shape each piece into a log and cut 3 pieces weighing 200-220g each. Knead them well.
4. For each tsoureki (sweet bread), you will need 3 pieces of dough. Place them in front of you. Take one piece of dough and roll it into a small log. Repeat with the other two. Then, take the first one and roll it into a long log about 40 cm long. Repeat with the others. Roll them out little by little because if you try to roll them out to the full length immediately, it will be difficult.
Place them vertically, side by side. Stick the end of the middle one and the left one to the first one. Make a fairly tight braid. Start from the strand on the right and bring it over the middle one. Then, do the same with the left strand. Repeat this until the tsoureki is finished. Tuck the ends from the top and bottom inwards so the tsoureki doesn't open up.
5. Place it on a baking sheet lined with non-stick parchment paper. When you have finished all 3 tsoureki, cover them with a towel or plastic wrap and set them aside for 1 – 1 ½ hours to rise, or continue the rising process in the oven set to 35-40°C, repeating the trick with the glass of water and the dough.
When they are ready to bake, brush them with the egg wash. Go over them twice with the egg so they brown nicely. Sprinkle them with the slivered almonds. Bake in a preheated oven at 160°C for 30-35 minutes. Remove the tsoureki from the oven and let them cool.
Store the tsoureki by wrapping them in plastic wrap.
