Once the yeast is ready, pour it into the flour, add the rest of the products (minus 1 yolk, use it for smearing later) and knead a medium soft dough.
Smear it with oil and leave to rise until doubled in volume. Melt the butter and add the oil to it.
Divide the risen dough into 3 parts. Roll the 1st one into a circle larger than the form in which you'll be baking. Smear it with the butter/oil mixture and sprinkle crumbled feta cheese.
Roll out the next one, place it atop the 1st, smear with butter and crumbled feta cheese again. Repeat for the last part of dough. Make a hole in the middle with your finger and start rolling it up from the middle going toward the edges.
Cut with a knife and twist the 2 ends in the opposite direction. Wrap into a spiral and place in an oiled tray, smear with the remaining butter. Leave to rise (or put in the oven at 122°F (50 °C)).
Beat the set aside yolk with 1-2 tbsp milk and smear the butter pita. Bake in a preheated 392°F (200 °C) oven about 50 min.