This soup is very rich in flavour but at the same time light and not filling. The earthy taste of the turnips combines well with the tartness of the apples. The tarragon sour cream makes a strong flavour complement. chicken stock can be substituted for water. I put the sour cream in a squeeze bottle and make designs with it on top of the soup as the soup is thick enough for the sour cream to stay in place. The soup alone, however is creamy enough; for those who don't eat dairy, simply garnish the soup with minced tarragon and lemon zest.