Put the potatoes in a large saucepan, cover with cold water and bring to the boil. Cook over a medium-high heat for 12-15 mins until tender, drain well and return to the pan. Mash until smooth. Spoon onto a large plate and cool slightly.

Meanwhile, heat the olive oil in a large, deep frying pan over a low-medium heat and cook the onions and red pepper with 3/4 tsp sea salt flakes for 10-12 mins, stirring occasionally until softened and slightly caramelised. Add the garlic, paprika and pul biber, and stir for 30 seconds or so until the spices are aromatic. Stir in the spinach and cook for 3-5 mins more to wilt. Stir in the warm mashed potatoes and mix until everything is combined, then spread out on the plate again and cool to room temperature.

Once the filling has cooled, stir in most of the halloumi and all the kaşar peyniri, mint and 3/4 tsp black pepper. Divide the filling into six equal portions. For the börek, crack 1 egg into a small bowl and mix with the yogurt, baking powder and oil. Crack the second egg into another bowl and whisk briefly. Line a large baking sheet with baking parchment.

Heat the oven to 200C/180C fan/gas 6. Lay 1 sheet of filo on a clean surface with a longer side facing you, and brush about a sixth of the egg and yogurt sauce all over it. Lay another sheet of filo on top, brush with melted butter, then spread one portion of the filling mix along the bottom edge nearest you. Roll the pastry up and away from you, enclosing the filling into a log shape. Curl the log around itself into a spiral, roughly 10cm in diameter. Pat it into shape using your hands – the warmth of your hands will help prevent it from splitting. Transfer to the middle of the baking sheet. Repeat with 2 more filo sheets and another portion of filling, but after rolling into a log, lift it onto the baking sheet, putting it at the end of the original spiral, and curl it around. Repeat with the remaining filo and filling until you have one large spiral. To freeze, cover with parchment, wrap and freeze on the tray until solid. Will keep frozen for three months.

Brush the rest of the melted butter over the börek, sprinkle over the remaining halloumi and brush with egg all over. Sprinkle over the sesame seeds and bake on the bottom shelf for 40-50 mins (or 50 mins-1 hr from frozen), or until golden brown all over. Serve warm with a green salad.