How to make
Sift flour with the salt onto a clean work surface and in a well in the center, tap an egg, add butter and stir slowly with a fork. Mix some cool water with the vinegar and gradually add it to the dough until it becomes homogeneous.
Knead the dough with your hands until it becomes smooth and elastic, but still remains soft and slightly sticky. Divide the dough into three equal parts, rub them with a brush with butter and cover them with a towel. Allow to sit for 30 minutes. While the dough sits, prepare the filling. Mix the soft butter with the cottage cheese, eggs, sour cream, salt and pepper.
Place one ball of dough onto a floured kitchen countertop. Start to roll it out as thinly as possible. Then, stretch it with the palms of your hands patiently, until you get it thin but not as thin as for a strudel. Cut off the thicker edges that have formed.
Smear half of the layer with the filling. Roll it up and shape it with your hands, gently squeezing it. Cut it in two and arrange in a buttered baking dish. You need to obtain rectangular pies whose ends are well stuck together so that the filling does not come out.
Do the same for the other dough balls as well. Smear the Štruklji pie with the cream, mixed with a little salt, sprinkle it with grated feta cheese and put cubes of butter on.
Place it to bake for about 40 minutes in a preheated 390°F (200 °C) oven. Serve the Štruklji slightly cooled.
