01 - In a large bowl, combine flour, yeast, sugar, and salt. Add olive oil and blend thoroughly. Gradually incorporate warm milk, kneading until a soft, elastic dough forms. Add extra milk as necessary to ensure smooth texture. Cover and leave in a warm location to rise 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 ground black pepper. Mix until evenly distributed to create a cohesive filling.
03 - Set oven to 375°F (190°C). Line a baking sheet with parchment paper to prevent sticking.
04 - Deflate risen dough and divide into 12 equal portions. Roll each portion into a ball and flatten into circles measuring 4 to 5 inches in diameter.
05 - Place a generous tablespoon of cheese filling in the center of each circle. Fold dough edges over the filling to form a triangle or oval, pinching seams securely to prevent leakage.
06 - Set shaped pastries evenly on prepared baking sheet. Whisk egg yolk with milk or water and gently brush the tops for a glossy finish.
07 - Transfer tray to oven and bake for 18 to 22 minutes or until surfaces are golden brown. Cool slightly on a rack before serving to ensure optimal texture and flavor.