First make the filling by cutting the leeks into medium-sized pieces, along with the green part.
Then put it in a pan on the stove and braise with 3-4 tbsp oil until semi-cooked.
Remove from the pot and add the yoghurt, feta cheese and 2 eggs. Stir the mixture well so that the feta doesn't melt. Your filling is now ready.
Open the packet of Phyllo Pastry sheets and sprinkle 3-4 tbsp filling onto each - either everywhere or just along the bottom end.
Carefully fold the 2 ends of the sheets toward the middle and then wrap it into a roll. Wrap the 1st one into a spiral and put it in the middle of an 11 3/4″ (30 cm) tray.
Wrap each subsequent roll around the first.
Once you've rolled up all the sheets, pour on a mixture of 2 eggs beaten in 2/5 cup (100 ml) water with 1-2 tsp oil.
Bake in a moderate oven (356°F (180 °C)) about 40 min. to a nice crisp.