Serbian Rolls with Cheese Filling

Crumble the cheese with a fork. Add a little salt if it's unsalted. Stir the egg white into it if the cheese is dry. The filling should be dense and salty. Dissolve the yeast with a little lukewarm milk in a small bowl, add a spoon of sugar and a tablespoon of flour, stir to a smooth paste. Leave at room temperature so the yeast activates and fills the bowl. Sift the flour with the salt. Add the activated yeast, the egg, the oil and the milk, then mix everything with a wooden spoon to get a smooth dough. The dough will look very soft and sticky at first, but as you knead it a bit it will start to come away from the bowl and thicken. You don't need to knead by hand, you can continue with the wooden spoon. Grease the kneaded dough with a little oil, cover the bowl and leave in a warm place for at least 1 hour, so the dough doubles in volume. Knead the dough again, divide it into 5 equal parts, shape them into balls. From each part you should make 8 rolls - 40 in total. Smooth each ball with your hands on a floured surface, then roll the dough into a circle a few millimeters thick. With a sharp knife cut the circle into 8 triangles. Take one triangle, stretch it in the air with your hands as much as possible, but carefully so as not to tear it. Put a little filling at the base of the triangle, then fold the edges of the base inward so the filling doesn't leak out, and roll it into a roll. Arrange the finished rolls in a previously greased and floured tray. Lightly beat the egg yolk with 1 tbsp of milk, then brush each roll with the mixture. Sprinkle with a little sesame, if desired. Arrange the margarine cut into small pieces between the rolls, then bake in an oven preheated to 180°C for about 20 minutes. Before serving, leave them to cool.