2) Beat the sour cream until thick (first it gets thinner, then if forms peaks). Season to taste with lemon juice and sugar.
3) Or:
Whip the cream to soft peaks, then add grated horseradish, vinegar and sugar to taste. The cream thickens quickly after the other ingredients are added.
4) Serve with a cucumber or lettuce salad with a vinegar or oil and vinegar dressing.