01 - In a large mixing bowl, blend all-purpose flour, instant yeast, sugar, and salt. Incorporate olive oil and gradually pour in warm milk, kneading until a soft, elastic dough forms. Add more milk if required. Cover the bowl and allow the dough to rise in a warm area for 60 minutes or until doubled in volume.
02 - In a separate bowl, combine crumbled feta, shredded mozzarella, parsley, nigella seeds if using, egg white, and freshly ground black pepper. Mix thoroughly until homogeneous.
03 - Preheat the oven to 375°F. Line a baking sheet with parchment paper to prevent sticking.
04 - Punch down the risen dough and divide it into 12 equal pieces. Shape each piece into a ball, then roll each into a flat circle measuring approximately 4 to 5 inches in diameter.
05 - Place a generous tablespoon of cheese mixture in the center of each dough circle. Fold the edges over the filling to form a triangle or oval, pinching seams securely to seal.
06 - Arrange the shaped pastries on the prepared baking sheet. Blend egg yolk with milk or water and brush the mixture over the tops for a glossy finish.
07 - Bake for 18 to 22 minutes until golden brown. Let cool slightly before serving.