Pour the cool water into a bowl, add the yeast and sugar. Leave it for 5 min. to rise and then begin adding the flour and salt.
Stir with a spoon until the mixture thickens and start to knead by hand until you get a soft dough, smear it with oil and leave it to rise for about 30 min.
Then divide it into 4 balls, roll out each one with a rolling pin, sprinkle with feta cheese, roll them up and arrange in the oven dish (from the middle going out).
Once you're done with that, smear the entire loaf with egg yolk on top and put to bake at 356°F (180 °C).