Cut the leeks into round slices and fry them until softened in 2 tbsp olive oil.
Beat the eggs in a bowl, add the yoghurt with baking powder, 1/2 the olive oil, crumbled feta cheese and sprinkle them with savory.
Stir everything and add the leeks. Butter a round 11 3/4″ (30 cm) tray, smear 1 of the sheets with a little olive oil and put part of the filling in it.
Wrap it into a roll and place in the middle of the tray.
Repeat this process for the other sheets and filling, arranging them around the middle one in the tray in a spiral shape.
Smear the phyllo pastry with beaten yolk and put it in a preheated 338°F (170 °C) oven for about an hour for it to gain a golden-brown crust.