Prepare the dough. In the bowl of a stand mixer fitted with the hook attachment, mix the flour, sugar, and yeast on low speed. Next, add the eggs and lukewarm water. Mix on low speed to combine all of the ingredients, then increase the speed to medium/high speed and knead for 5 minutes. After 5 minutes, add the salt. Turn on your mixer to medium speed and add the butter pieces, one at a time. Once all of the butter is incorporated into the dough, knead on medium/high speed for 5 more minutes.

Transfer the dough to a greased bowl. Cover it tightly with plastic wrap and refrigerate the dough overnight, or at least 6 hours.

Prepare the filling. The next day, prepare the filling. Dice 1 1/2 packs of halloumi into 1/2-inch cubes. Finely grate the remaining 1/2 halloumi. Combine the diced halloumi, grated halloumi, chopped onion, mint, and salt in a mixing bowl.

Line a 9 x 4-inch loaf pan with parchment paper, allowing 2 inches of overhang on each of the long sides. Lightly grease, and set aside.

Roll out dough and shape. Remove the dough from the refrigerator. It should have risen slightly. On a well floured surface (the dough will be a little sticky), roll the dough out into a 16-inch square and spread the filling over the dough, leaving ½-inch border uncovered. Starting from one end, tightly roll the dough into a log. Use a sharp knife to trim off the edges and cut the log in half. Place one half on top of the other to a form a cross shape. Twist both ends to form a spiral and transfer the dough the prepared loaf pan.

Cover the loaf pan with a clean kitchen towel and allow it to rise for 1 ½ hours. 

Preheat oven 375°F.

After the second rise, make an egg wash by whisking the egg yolk with 2 tablespoons of water. Brush the top of the dough with egg wash and sprinkle the sesame seeds. Bake for 40-45 minutes.

Allow the bread to cool in the pan for 15 minutes, then use the parchment paper to lift it out of the pan. Discard the paper and let the loaf cool on a wire rack before slicing it.