You people made me want sour cream, so I went into the kitchen and grabbed my likeliest culprit for pairing with sour cream -- beets.
I had no fresh beets left, nor any pickled (or I would've just eaten them with sour cream on top), and I wanted something smooth, so I blended a can of beets with a splash of balsamic vinegar and a scant cup of buttermilk (probably between 3/4 and 1 cup), then topped it with some sour cream. To me, buttermilk is just like liquid sour cream, anyway.