In a large bowl dissolve a small piece of yeast in lukewarm water. Add the lukewarm milk, Horio Koroneiki variety, salt and some flour and start kneading while adding as much flour as needed, so that the dough is smooth but not sticky on our hands.
When the dough is ready, cover it with a towel and let it rest in a warm place until risen and doubled.
Clean the onions and cut them in thin slices. Put them in a bowl, add some coarse salt, pepper and Horio Koroneiki variety and rub them with the hand.
With a brush, grease a baking tray, put the dough inside and open it using your fingers in order to spread it across the tray’s surface.
Use a spoon to apply the tomato paste on the dough. Add the onions and Horio feta cheese (or Horio light white cheese), grated by hand. Finally, add the sliced tomatoes and flavor it with thyme.
Bake in preheated oven for about 50 minutes at 180C.