In a cup or small bowl mix milk, 1 spoon of sugar and 1 spoon of flour with yeast. Place it in warm place and wait till the mixture raise and double itself.
Sift the flour, add chopped butter, mix, add yolks and yeast mixture when it's ready.
Knead uniform, smooth dough.
Place it in fridge for 1 hour, till it doubles it's size.
Meanwhile, mix apple, pear, cinnamon and lemon juice.
After 1 hour, roll out the dough (about 5mm thick), cut out rectangulars, place apple & pear mixture in the middle, lift all four tips up and pinch the end to form a "pouch".
Whip eggs whites with a fork, brush each "pouch" with egg's whites and sprinkle with sugar.
Bake in preheated oven, in 180 C degrees, about 10 min, till golden brown.