Maddy Prior and June Tabor’s Silly Sisters is a magical hinge album, a meeting of two transcendent voices and a jolly band of British folk masters. Recorded in 1976 but somehow outside of time, its ancient songs, close harmonies, and loose, luminous performances summon something older than the British folk revival itself. Fifty years on, it remains a timeless gem hiding in plain sight: raw, sophisticated, mysterious, and still not quite given its due.