The asteroid 486958 Arrokoth was discovered to be binary by astronomers lugging a bunch of telescopes around (I think) camping with them. The timing offered additional astrometry for the orbit determination before New Horizon's flyby, and it also served to put an upper limit on any dust or debris cloud around the object that might suggest a farther flyby distance be considered.
Their hard work certainly paid off and an outline of the object was reconstructed, showing that it was likely a binary; two circular objects. This posed a bit of a mystery because there wasn't any periodic variation in brightness detected that would suggest rotation, but that's a different story.
Is this the only solar system object that was discovered to be binary (or higher) via occultation?