  We present optical/UV observations and the spectroscopic classification of
the transient AT2023vto as a tidal disruption event (TDE) at z = 0.4846. The
spectrum is dominated by a broad He II $\lambda$4686 emission line, with a
width of ~ $3.76 \times 10^4$ km/s and a blueshift of ~ $1.05 \times 10^4$
km/s, classifying it as a member of the TDE-He class. The light curve exhibits
a long rise and decline timescale, with a large peak absolute magnitude of
M$_g$ ~ -23.6, making it the most luminous of the classical optical TDEs (H,
H+He, He) discovered to date by about 2 mag (and ~ 4 mag compared to the mean
of the population). The light curve exhibits a persistent blue color of g - r ~
-0.4 mag throughout its evolution, similar to other TDEs, but distinct from
supernovae. We identify the host galaxy of AT2023vto in archival Pan-STARRS
images and find that the transient is located at the galaxy center, and that
its inferred central black hole mass is ~ $10^7~M_{\odot}$. Modeling the light
curves of AT2023vto, we find that it resulted from the disruption of a ~ 9
$M_{\odot}$ star by a ~$10^7~M_{\odot}$ supermassive black hole. The star mass
is about 5 times larger than the highest star masses previously inferred in
TDEs, and the black hole mass is at the high end of the distribution. AT2023vto
is comparable in luminosity and timescale to some putative TDEs (with a blue
featureless continuum), as well as to the mean of the recently identified
population of ambiguous nuclear transients (ANTs), although the latter are
spectroscopically distinct and tend to have longer timescales. ANTs have been
speculated to arise from tidal disruptions of massive stars, perhaps in active
galactic nuclei, and AT2023vto may represent a similar case but in a dormant
black hole, thereby bridging the TDE and ANT populations. We anticipate that
Rubin Observatory / LSST will uncover similar luminous TDEs to z ~ 3.
