Activate the yeast with the warm milk, sugar and a little flour.
Once it bubbles, knead a smooth dough with the remaining ingredients. Leave it to double in volume, then roll out a sheet about 1/4" thick from the dough. Smear it generously with the melted butter.
Make cuts along half the sheet with a pizza cutter.
Crumble feta cheese over half the sheet and wrap it up into a roll, starting from the uncut side. Twist the roll into a spiral and put it in an oven dish with baking paper.
Leave it to rise in a warm room at 77°F (25 °C). Once the loaf rises, smear it with the beaten together yolk, milk and oil. Sprinkle with sesame and poppy seeds if desired.
Bake 35-40 min. in a preheated 320°F (160 °C) oven.