Mix together yeast, warm water, and 1 teaspoon sugar and set aside to rise, approximately 10 to 15 minutes.
Meanwhile, melt the butter and warm up the milk to a simmer in separate saucepans.
In a mixing bowl, beat the eggs with the remaining 1 cup sugar, whiskey and vanilla extract. Then slowly add the hot milk, beating constantly (to gently warm the eggs), followed by the melted butter until well combined. Then beat in the yeast mixture. The liquid mixture should be fairly warm.
In a large mixing bowl, combine the flour (weighing is more accurate than measuring in cups), mahleb, baking powder, and salt. Create a well in the center of the dry mixture and pour in the liquid mixture. Use a large spoon to gently mix the dry mixture into the liquid, starting from the center and moving outward until all the dry mixture is moistened. Start using your hands to finish mixing and knead the dough. Continue kneading until you have a soft, pliant, and slightly tacky but not-too-sticky dough.
Place the dough in a large greased bowl (make sure that the bowl is considerably larger than the dough, as it will rise), and wrap tightly with plastic wrap or cover loosely with a clean kitchen towel.
Briefly heat the oven and then turn it off so it's slightly warmer than room temperature but not hot. Place the dough in the warmed oven and allow it to double in size, approximately 1 1/2 to 2 hours. Check on the dough occasionally to see its progress.
On a large clean work surface, shape the dough into desired shapes as follows.
To make the braid shape: Roll out a piece of dough between your hands and the work surface until you have a 1/2-to-3/4-inch thick rope. Cut off 1/3 of the length of the dough and attach it to the center of the longer piece by pressing the pieces together. Very loosely braid the ropes together (the braid will proof and get bigger later, so don’t braid tightly). Press the ends together to “seal” the braid.
To make the snail/spiral shape: Roll out a piece of dough between your hands and the work surface until you have a 1/2-to- 3/4-inch thick rope. Gently and loosely wrap the dough around itself starting from the center and moving outward. Tuck the end under the dough and gently press to seal it closed.
To make a chorek person: Lightly flour your work surface and hands, and roll out a piece of dough between your hands and the work surface to create an even cylinder. Pat the dough out into a rectangle with the long sides on either side. Use a bench scraper or knife to cut a slit at the bottom (for the legs), 2 slits on either side (for the arms) and another 2 slits slightly above the arms (for the head). Tuck under the pointy ends of the arms. Adjust the dough around the head to either make it look like hair (for a girl), or tuck the points under the head to make it round (for a boy). Use whole cloves for the eyes, and red M&Ms for the mouth. Very carefully use a large floured spatula to transfer chorek people from the work surface to the baking sheet. They are more fragile than the other shapes. Remove the clove eyes before eating.
Place assembled choreks onto parchment paper-lined or greased baking sheets (leaving adequate space between the choreks as they will rise and expand further during baking). You will need about 3 to 4 half sheet pans for this amount of dough depending on the shapes you choose to make.
Place baking sheets back into a warmed oven (make sure the oven is turned off) to allow the choreks to proof, approximately 15 to 30 minutes. Remove from the oven.
Preheat the oven to 350 degrees F. Beat the egg, egg yolk and sugar together and brush all the choreks (including the sides) with the egg wash mixture. Be careful with the red M&Ms on the chorek people's mouths so you don't brush red coloring onto the dough; just brush around the mouths instead of over them. Sprinkle with sesame seeds (but omit sesame seeds for chorek people shapes).
Bake choreks for 28 to 32 minutes until golden brown (baking time will be dependent on the size of your choreks and the shapes you've made), rotating the baking sheets from top to bottom and front to back halfway through to ensure even baking. The chorek people typically bake faster than other shapes.
Allow choreks to cool completely before serving. Choreks should be stored at room temperature, but can be warmed up before eating, if desired. They can also be frozen, thawed, and enjoyed at a later date. Refresh previously frozen chorek for a few minutes in the oven before serving.