Sift in the flour, sugar and salt. Dissolve the yeast in approx. 10 tablespoons of milk and stir into a pulp with a little flour, cover with a little flour. Let rest for about 15 minutes until the flour crust starts to crack.
Add the porridge, the rest of the milk, the water, an egg and an egg white in a well in the flour. Knead into a soft dough and cut into 3 parts. Roll out each part and brush with soft butter. Knead together again and roll out into a round shape (approx. 1 cm thick). Cut into 10 triangles (like a cake).
Crumble a piece of feta cheese over the wide part of each triangle. Roll up towards the middle. Brush a mold with oil and insert the parts. Let rise covered for about 1 hour. Brush with egg yolk.
Preheat the oven to 180 ° (top / bottom heat). Bake on the bottom rack for about 60 minutes until golden brown. When the pita breads are ready, sprinkle with water and cover with a cloth.