Sprinkle the yeast and sugar over the warm water in a small bowl. Let this mixture sit until it begins to bubble, about 5 minutes.

Combine the flour, salt and mahleb in a large mixing bowl. Add the butter and work it into the flour using your fingers. Make a well in the center and pour in the yeast mixture, cooking oil and 1/2 cup of cold water. Stir together to form a soft dough, adding more cold water if necessary. Knead the dough on a lightly floured surface until it is smooth and pliable. Clean and lightly butter the mixing bowl, put in the dough and turn it around to coat it thoroughly. Cover the bowl with a damp towel and let the dough rise for 2 hours.

Preheat the oven to 400°F.

Knead the dough for several minutes to eliminate any air pockets. Break off walnut-sized pieces, roll each into a ball, then roll them between your palms to form a foot-long snake. Fold each snake in two, then twist gently and pinch the ends together. Put the choreg onto a lightly greased or parchment-lined baking sheet, brush with egg glaze, and sprinkle with sesame seeds. Set on top of the hot oven to rise for 15 minutes, then bake for 15 minutes, until golden. Pile up the choregs onto a single baking sheet. When all are finished, turn off the oven, open the door and put the baking sheet back into the oven. Let the choregs sit there until they are completely dry and cool, then pack in an airtight container.