In a bowl mix with a food processor milk in sachet sauce until it turns into a thick cream . Add the feta cheese, the cheddar cheese, the yogurt and the oregano and mix well in order to prepare the filling. Roll out the puff pastry first sheet and spread in a rectangular pan , pierce with a fork and add the filling. Cover with the second sheet of puff pastry and carefully fold the edges to be joined with the bottom sheet so as for the filling not to overflow during baking .Pierce with fork and whipe the cover sheet with some egg or a little olive oil . Bake for about 1 hour at 180 degrees .