Peel the leeks and cut them in the middle, then in small pieces. Put the chopped leeks in water to thorogly clean them
After the leeks are cleaned, in a hot pan with olive oil and medium-low heat, let them sweat. Do not forget to make sure to mix them every once in a while. About half-way add some salt and a generous amount of freshly ground black pepper
The leeks are done when they are soft. It will taka e bit of time - around 30 minutes in a medium low heat in the pan.
Once the leeks are done, take them off the heat and let them sit for a bit.
Preheat the oven at 200 degrees
In a big bowl mash the feta cheese and add the egg and the milk. Mix them throughly
Add the leeks in the feta mixture and combine.
In an oven tray, covered with some parchment paper, lay in one of the pastry dough
Throw in the leek and feta mixture and spread it around. Keep in mind that you should leave some space on the sides, so you can stick the top pastry paper with the bottom one
Cover the whole thing with the other pastry dough and with a fork press on the sides so a pocket is formed.
Make some egg wash and spreadh on top of the pastry for a golden crisp - alternatively do not bother with this step.
With a fork, make 3-4 holes on the pastry dough
Place it in the oven for 15-20 minutes. It is done once the bottom is not soggy anymore.
