1.Preheat the oven at 375 degrees F.
2.Chop the onion and the leeks.
3.Heat oil in a pan and add the leek,onion,salt,pepper.
4.Cover and saute over low heat until the leeks and onions are very soft.
5.Once cooked and caramelized set them aside to cool.
6.For the filling put the beaten eggs in a bowl, add yogurt, mozzarella,thyme, nutmeg and mix well.
7.To this mixture add the leeks mixture and give it a good stir.
8.Transfer the contents to the pie shell and sprinkle with Parmesan cheese.
9.Bake in the preheated oven for 40 to 45 minutes until filling is set, crust is golden and cheese is lightly browned.
10.Let it sit for 10 minutes.