  We report the discovery of a 1201 s orbital period binary, the third
shortest-period detached binary known. SDSS J232230.20+050942.06 contains two
He-core white dwarfs orbiting with a 27 deg inclination. Located 0.76 kpc from
the Sun, the binary has an estimated LISA 4-yr signal-to-noise ratio of 40.
J2322+0509 is the first He+He white dwarf LISA verification binary, a source
class that is predicted to account for one-third of resolved LISA ultra-compact
binary detections.
