I don't know if recitals of folk songs by Paul Robeson count as folk music. But he did just that, and, at least in the late-60s was was well thought of for those concerts. Somewhere in a room I not able to easily get to are a couple of Robeson LPs. The accompaniment on those recordings was a sole piano, if not on all tracks on the vast majority of them. I think others gave similar recitals, but none come readily to mind.