Substitution Solution

Lemon juice also works to sour the milk for buttermilk substitution. Those substitutions work for baking. If you're making a sauce or not cooking with it, I'd be wary.

I don't know about substitution, but did you know you can make your own buttermilk? Put 1TBS vinegar in a glass measure and then fill with milk to 1 cup and let stand for 5 minutes. My only thought about subbing sour cream for buttermilk is the buttermilk has acid in it and is thinner. Maybe thin the sour cream with vinegar?