Place the hazelnuts on a baking tray and
To make the crème pâtissière, warm the milk in a saucepan over low
Meanwhile, combine the egg yolks, cornflour, flour and icing sugar in a mixing bowl and whisk until smooth. Ladle about
Sift the flour into a mixing bowl, make a well in the middle, break in the eggs and then add the baking powder, vegetable oil and yoğurt. Knead the dough for about 10 minutes, or until the dough is soft and stretchy. Cover the bowl with a damp cloth and rest for 1 hour to expand.
Sprinkle some flour on your work surface. Divide the dough into twenty pieces and roll into balls. With floured hands or a rolling pin, flatten one ball into a round
Melt the butter in a frying pan over medium heat (or microwave for 30 seconds). Brush each round with the butter and then place the rounds on top of each other to make a stack. Press the stack down and spread the dough out with a rolling pin, as thin as possible. Brush with butter and roll into a log. Slice into three equal pieces, wrap each piece in plastic wrap and refrigerate for 1 hour to rest.
Remove the chilled dough from the fridge (or freezer if using store-bought puff pastry) and leave to warm to room temperature. Grease a
Roll out the second and third pieces of puff pastry to the size of your tray, and brush the top with butter. Place the second puff pastry layer on top of the first, sprinkle with another third of hazelnuts, and then place the final pastry layer on top.
Cut the stacked dough into
Sprinkle the remaining hazelnuts on top of the börek, dust with cinnamon and icing sugar, then serve warm.