Beat the eggs well, add the yoghurt and baking powder and mix again.
Lay out the phyllo pastry sheets 1 by 1 and smear them with butter. Then pour a little of the mixture on it. Crumble feta cheese on top and roll it up.
Do this for all of the sheets. Once rolled up, smear them with the remaining mixture on top. If you like you can place a few small lumps of butter in several spots. Bake in a preheated 392°F (200 °C) oven until ready.