Linked from
The 9 pages that link to Sour cream, each with the reason it gives.
BliniRelated: Its acidity and richness make it a common topping for blini.
ChivesRelated: Its richness and tang complement the mild onion flavor of chives.
BorschtRelated: A spoonful often softens borscht’s acidity and adds richness.
Ranch dressingRelated: It is a common alternative or addition to buttermilk for a thicker dressing.
PelmeniRelated: Its acidity and richness make it a common accompaniment to pelmeni.