1. Sour cream
1 cup
sour cream
Best swap: Sour cream. Use 1 cup sour cream per 1 cup.
Plain yogurt adds moisture and tang to bakes and creaminess to savoury dishes. Other cultured dairy stands in for it easily.
Sour cream is the closest swap, cup for cup, in baking and savoury dishes. Buttermilk works in batters if you slightly reduce another liquid.
Yes, one-to-one. It has similar acidity and thickness, just a little more fat, so results are slightly richer.