Add 600 g potatoes to a large pot of cold water. Bring to a boil, then cook until knife-tender (about 20 minutes).
Once the potatoes are cooked, drain in a large colander. Once cool, carefully remove the skins.
In a large frying pan over medium heat, add 1 tablespoon olive oil. Saute 80 g onion* (chopped) and 2 garlic cloves (chopped) until aromatic and softened.
Add 1 teaspoon red pepper flakes, ½ teaspoon red chilli powder, ½ teaspoon smoked paprika, and ½ teaspoon cumin powder to the pan. Saute for a few seconds, being careful not to burn. Turn off the heat.
Add the potatoes to the pan and roughly mash them. Add the seasonings—½ teaspoon black pepper, Sea Salt to taste, and 2 sprigs thyme — and mix all the spices and seasonings into the potatoes.
Make the Pastry Sauce
Whisk together 250 ml oil, 1 ¼ teaspoons vinegar, 1 ¼ tablespoons yoghurt, and 2 ¼ tablespoons plain flour (AP) in a medium-sized bowl.
Roll and Shape the Borek**
Cut 400 g yufka pastry sheets into small triangles. Brush one triangle completely with your pastry sauce. Layer another triangle on top, brushing with a thin layer of sauce.
Add a small amount of potato filling in a strip along the larger side of the triangle.
Fold the sides of the pastry over the potato filling, then roll up the pastry (like a spring roll). If needed, you can add water or pastry sauce to seal the ends.
Bake the Borek
Preheat your oven to 180℃ (356℉).
Crack an egg and separate the 1 egg yolk into a small bowl. Whisk until smooth.
Place the rolled borek onto a lined tray and brush the tops with egg yolk.
Sprinkle a mixture of seeds on top of the borek — I used 1 ½ teaspoon nigella seeds, ½ teaspoon white sesame seeds, and ½ teaspoon poppy seeds.
Bake for around 40 minutes, or until evenly golden brown.
Notes
* 80g of onion usually equals about 1 medium onion.** Please see the step-by-step pictures further up the post for a visual representation of how to shape the potato borek.