For the dough: mix the flour with the salt and add the butter, cut into pieces. Place everything in a blender or use a hand held blender to blend until you get a crumbly mixture.
Add the cold water and blend some more. Cover the dough with foil and place it in the refrigerator for 30 minutes. After removing, roll it out into a crust and put it in a round oven dish, pressing it snugly along its walls.
For the filling: clean the leeks and chop them into thin strips. Melt the butter and add the leeks and thyme. Cover with a lid and leave it to stew for 10 min and then cool. Then add the lemon zest and juice, parmesan, sour cream, egg, stir until everything is absorbed and finally add the diced feta cheese.
Add salt and pepper. Pour the mixture over the crust and top with the yolks beaten with 1 tablespoon of water. Bake at 392°F (200 °C) for 20 minutes, then reduce to 356°F (180 °C) and bake for another 15 minutes.