Starter: In a medium size bowl, active dry yeast, sugar, flour, and lukewarm milk. Make sure that your milk is not too hot, or else you will kill the yeast. Cover the bowl with plastic wrap and set mixture aside for 15 minutes. The yeast will begin to bubble and activate.
Grind the spices by placing the mahlepi, mastic gum, cardamom pods, and salt in the bowl of a small food processor or blender. Process until the mixture is powdery.
Sift the flour and ground spices in the bowl of a stand mixer fitted with the hook attachment.
In a separate bowl, whisk together the eggs, sugar, vanilla extract, orange zest, and milk.
Add the starter to the sifted flour/spice mixture. Add the egg mixture and then the melted butter. Using your dough hook attachment, mix on low speed for 10 minutes. Increase the speed to medium and knead for another 5 minutes. The dough will start to pull away from the sides of the mixing bowl.
Transfer the dough to a large greased bowl. Cover with a clean kitchen towel or plastic wrap and place it in a dark, warm spot of your kitchen (like your oven or in the microwave). Let the dough rise for 2 hours. After 2 hours, the dough will double in volume. Uncover it and punch it down. Knead the dough by hand for about 5 minutes. Then, cover the bowl and let it rise for another 30 minutes.
After the second rise, transfer the dough onto a lightly floured surface. Divide the dough in half. Each half will make 1 loaf. For the classic three-strand braid, divide a half into three balls. Roll each section into long ropes, then form a braid. Repeat the process with the second half. Check out the video for a 4-strand braid.
Once your loaves are shaped, place them on a parchment lined baking sheet. Cover the baking sheet and let rise for another 30 minutes.
Preheat oven to 350 degrees F.
Gently brush with egg wash. Sprinkle with sliced almonds. Bake in preheated oven for 35-45 minutes, or until golden brown.
Transfer bread to a wire rack and allow to cool for about 30 minutes. Slice and enjoy!