To make the dough: In a bowl, combine the flour, beaten egg, white vinegar, sugar, and salt. Add water as needed to create a stiff dough. Start with ½ cup of water and add more as needed until you have an elastic, uniform dough. Keep the dough firm and stiff; do not add too much water.
Knead the dough until smooth and elastic, about 5 minutes. Wrap the dough in plastic wrap and let it rest at room temperature for at least 20 minutes. This is an essential part of the process.
The next step is incorporating the fat into the dough. The fat softens and moistens the dough while tenderizing the gluten structure. Add the butter and continue kneading thoroughly until it is completely incorporated and the dough is smooth, shiny, and elastic.
Cover with cling film and refrigerate overnight. The dough can be refrigerated for up to 3 days before using. It is ideal for any recipe that calls for puff pastry and is the easiest alternative to traditional puff pastry.
To make the filling: Add the sunflower oil to a saucepan and warm it for a few seconds before adding the flour. Once the flour has been added, whisk it together with the oil to form a paste, then let it cook for 30 seconds.
Add 1 cup of the milk and whisk constantly to remove any lumps. If you still have some lumps, don’t worry—they will dissolve completely once you add the cheese. Keep stirring until the mixture thickens completely.
Add the cheeses and nigella seeds (if using), and whisk constantly over medium heat until the cheese melts and everything is well combined.
You should end up with a smooth, pliable, and stretchy mixture with no lumps. Leave it to cool completely before filling the sambousek.
To Put Together: Make the Rectangular Shapes
Remove the dough from the refrigerator, knock it back, then remove it from the bowl and divide it into two equal portions.Working with one portion at a time, roll the dough out on a lightly floured work surface to a thickness of 1/4 inch / 6 mm using a rolling pin. The dough can become sticky, so keep some extra flour nearby and dust the work surface as needed.Using a pizza cutter, score the dough into 5 x 5 cm (2 x 2 inch) squares. The exact dimensions are not important, but the thickness is. You can make the squares larger if you prefer. Fill each square of dough by placing a heaping tablespoon of filling in the center.
Make the flour slurry by combining flour and water in a small bowl to form a moderately thick consistency. Brush the borders of each square with the slurry. This extra step helps bind the edges together and prevents the filling from leaking out during frying.
Fold two corners over the filling to form a small rectangle. Using a fork, crimp the edges of the sambousek together to seal. Make sure the turnover is tightly sealed to help prevent the filling from leaking out while frying.
Ready to fry or freeze!
Alternatively, you can garnish the center of each sambousek with nigella seeds. Brush the center with the flour-and-water slurry, then sprinkle with nigella seeds, if desired.
Heat the oil to the appropriate frying temperature, about 350°F/180°C. When ready, carefully add a few sambousek, making sure not to overcrowd the pan. Fry for 2–3 minutes, then flip. Once both sides are golden brown, transfer the sambousek to a plate lined with paper towels. Repeat with the remaining sambousek.
Alternatively, you can shape the sambousek/börek into a half-moon shape, just like you would when making empanadas! Here’s the technique:
Remove the dough from the refrigerator, knock it back, then remove it from the bowl and divide it into two equal portions. Working with one portion at a time, use a rolling pin to roll the dough out on a floured work surface to a thickness of 1/4 inch (6 mm).
Using a 4-inch (10 cm) cookie cutter, cut the dough into circles. Gather any scraps, reroll the dough, and cut out more circles.
Fill each circle with a heaping tablespoon of filling, placing it in the center.
Carefully fold the circle in half to form a half-moon shape. Press the edges firmly to seal. Crimp the edges with the back of a fork.
Heat the oil to the proper frying temperature, usually 350°F/180°C. When ready, carefully add a few sambousek to the oil, making sure not to overcrowd the pan. Fry for 2–3 minutes, or until golden, then flip. Once both sides are golden brown, transfer the sambousek to a plate lined with paper towels. Continue frying the remaining sambousek in batches.