Preheat the oven at 200 degrees Celsius.
Cut the feta cheese, and then mash it with a fork.
Add the cottage cheese with the feta cheese, and stir.
In a big bowl whip the four eggs and the sour cream.
Pour the egg and sour cream mixture in the cheese mixture, add one fourth of a teaspoon of salt, and stir together.
Brush a baking form with some oil. Put two layers of Filo dough in the form.
Brush the dough with some oil and sprinkle a few drops of sparkling water and some salt on the dough.
Add some of the filling mixture on the dough.
Continue the procedure with the dough and filling, until you only have two dough rolls left as the top layer.
Whip the egg yellow with a few drops of sparkling water and brush it on the top layer of the pie.
Place the pie in the lower part of the oven for thirty minutes. Then lower the temperature to 180 degrees Celsius and take out the pie after ten minutes.
If you like the pie warm serve it directly, otherwise let it cool down first.