Crumble the feta cheese and add the eggs and yoghurt in which you've beaten the baking soda.
Stir the mixture until homogenized.
Mix the butter and oil, pour hot water over them.
Smear a phyllo pastry sheet with the oily mixture, spread it out along the entire surface.
Place a 2nd sheet on top and smear again.
Put some of the filling at one end, roll it up and place in a buttered round tray.
Arrange the rolled up sheets 1 by 1 in it, starting from the outside and going in.
Roll the final sheet up into a spiral and place in the middle.
Mix the rest of the filling and oil/butter and smear the phyllo pastry on top. Put it in a warm oven and bake at 356°F (180 °C) for about 35 min.