In a shallow bowl, combine milk with the 1 tablespoon of sugar. Mix and sprinkle yeast on top.
Leave to rest for 5-10 minutes, until foamy.
In the bowl of an electric mixer, beat eggs well until frothy.
Add butter, sugar, vanilla and mahleb. Mix well until thoroughly combined. SEE NOTE
Add salt and flour.
Knead for 10 minutes, until dough is smooth, soft and elastic. Dough should be soft, but not sticky.
Place in a greased bowl and cover with plastic wrap sprayed with non stick spray.
Cover with a kitchen towel and leave to dry in a warm place for about 5 hours, until doubled in volume.
Divide dough into 3 equal portions, each weighing approximately 1 lb. 3 oz.
Roll each portion into a long rope, about 17".
Braid the 3 ropes into one long braid.
Place diagonally on a cookie sheet lined with parchment paper or sprayed with non stick spray. SEE NOTE #2
Cover and let dough rise again for 1 hour.
Preheat oven to 350 F.
Brush loaf with egg wash.
Bake for 40-45 minutes until golden and crusty on top.