Add the salt to the water. Sift flour into a bowl. Make a well in center; add egg yolk and butter. Combine flour, egg yolk, butter. Add the salted water. Mix until it starts to pull away from the sides and stick together. Using hands, knead the pastry, until it's elastic, about 4-5 minutes. Let stand for 1 hour, covered with a cloth or plastic wrap.
Add a heaping tablespoon or so of the beef filling just to the left of the center of each square. Using your fingers, moisten the edges of three left edges of dough with water. Carefully fold over the right side keeping the filling inside away from the edge so that you get dough on dough to seal. Push down to seal with fingers.