Preparation

Make the dough

• In a small saucepan over medium heat, bring the milk to a boil. Let cool until just warm (110°F), about 30 minutes. Meanwhile, combine 1 cup of the flour with the yeast in the bowl of a stand mixer. Stir in 1/2 cup very warm water (about 120°F), and form into a ball. Cover the bowl lightly with plastic wrap. Set the bowl in a warm spot until the mixture has visible bubbles on its surface, about 30 minutes.
• Put the bowl in the mixer stand, and fit the mixer with the dough hook. On medium speed, beat in the egg yolks, sugar, butter, and salt, scraping the bowl occasionally. With the mixer running, add the milk and continue to beat until combined (it’s fine if there are a few lumps), about 2 minutes. Gradually add the remaining 2 cups flour. Raise the speed to medium-high, and knead until the dough is smooth, about 5 minutes. The dough will be soft and may not form a ball. Stop the mixer, add the lemon and orange zest and mahleb, and continue to mix until incorporated, 1 minute.
• Lightly coat a bowl with the cooking spray. Transfer the dough to the bowl and cover with plastic. Let rise in a warm place until the dough is doubled in size, 60 to 75 minutes.

Shape the dough

• Line a large rimmed baking sheet with parchment. Set aside.
• Gently scrape the dough onto a lightly floured surface (try not to use more than 1 to 2 Tbs. of extra flour). Divide the dough into thirds.

• Stretch each piece of dough to a 20- inch length, then gently braid them together.

• Shape the braid into a round, leaving the center empty as if you’re making a wreath.

• Carefully transfer the dough to the prepared baking sheet. Gently press the hard-boiled eggs into the dough at even intervals. Cover with plastic wrap, and set in a warm place until the dough rises by 50 to 75 percent, about 50 minutes.

Bake the bread

• Position a rack in the center of the oven, and heat the oven to 350°F. Just before baking, whisk the egg with 1 Tbs. water in a small bowl, and use a pastry brush to brush the dough with the egg wash. Sprinkle the sesame seeds on top. Bake until a wooden skewer inserted in the center comes out with only dry crumbs and the top is a deep golden amber, 25 to 35 minutes. (If the loaf starts browning too deeply, cover the loaf with foil halfway through.) Let cool at least 20 minutes before serving. Store the bread in an airtight container at room temperature for up to 3 days.