cupful of vegetable broth to a boil. Trickle, stirring, 0.5 cup
of the same cold broth shaken with 2 tea-spoons of flour into
it. Bring to a boil. When the resulting broth thickens, add 1
table-spoon of butter, sour cream, and tomato paste. Heat
without bringing to a boil. Instead of tomato paste you can use
fresh tomatoes. Cook them in butter and rub through a sieve.