How much water in potato-leek soup (Vichyssoise)?
I'm not sure if it's a typo but the recipe surprises me, traditionally (as far as a 100ish year old dish can be "traditional") vichyssoise would have chicken stock or seasoned milk as the liquid base. 

For that quantity of potato and leek I would estimate 0.6->0.75L of liquid so it is possible it is a typo.