In a bowl, beat the eggs well, then add the yoghurt and stir well again.
Melt the butter and add it. Once it cools, add the yeast which you've dissolved in warm water, the crumbled feta cheese, flour and knead a dough. Leave it to rise for 20-30 min., then tear it into balls, arrange them in a buttered tray and leave to rise.
Once risen, smear them with an egg yolk and bake in a moderate oven until ready.