Preheat the oven at 200 degrees Celsius.
Mash the feta cheese together with the ricotta cheese.
Whip together the eggs and the sour cream.
Mix the cheese and the sour cream mixtures together.
Brush a baking form with some olive oil.
Put 2 layers of filo dough in the form. Brush it with some olive oil. Add some of the cheese filling on the dough and sprinkle some sparkling water and salt.
Brush the top with the egg yellow and sprinkle some sparkling water on top.
Place the pie in the lower part of the oven for 30 minutes, than lower the temperature to 180 degrees Celsius. Let the pie in the oven for another 10 minutes.