Sift the flour, add sugar and salt. Dissolve the yeast in about 10 tablespoons of milk and stir into a paste with a little flour, cover with a little more flour. Let rest for about 15 min until the flour crust cracks. Add the porridge, the remaining milk, the water, one egg and one 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 softened butter. Knead again and roll out round (about 1 cm thick). Cut into 10 triangles (like a pie).
Crumble a piece of feta cheese over the wide part of each triangle. Roll up towards the center. Coat a baking pan with oil and place the pieces inside.
Cover and let rise for about 1 hour. Brush with egg yolk. Preheat the oven to 180° (top/bottom heat). Bake on the lowest rack for about 60 minutes until golden brown. When the pita breads are ready, sprinkle with water and cover with a cloth.
