While butter is melting, in another very large bowl (I used a big lobster pot) combine flour, salt, and mahleb if using, and set aside.
In a large bowl, whisk sugar and eggs together, and set aside.
Line cookie sheets with parchment paper and preheat the oven to 375 F degrees.
Beat 1-2 eggs with a splash of water or milk for the egg wash. Brush tops and sides of choreg with egg wash, and then sprinkle with sesame seeds. Bake for 20-25 minutes, rotating once, or until tops just turn brown.
Remove pan from oven. Carefully slide the parchment paper off the baking sheet, and cool choregs on parchment.
Once completely cooled, store in airtight storage bags or containers. They should keep for about 1 week at room temperature, or can be frozen for 3-4 months.