  This study is part of the project ``CORE'', an IRAM/NOEMA large program
consisting of observations of the millimeter continuum and molecular line
emission towards 20 selected high-mass star forming regions. We focus on
IRAS23385+6053, which is believed to be the least evolved source of the CORE
sample. The observations were performed at ~1.4 mm and employed three
configurations of NOEMA and additional single-dish maps, merged with the
interferometric data to recover the extended emission. Our correlator setup
covered a number of lines from well-known hot core tracers and a few outflow
tracers. The angular (~0.45"$-$0.9") and spectral (0.5 km/s) resolutions were
sufficient to resolve the clump in IRAS23385+6053 and investigate the existence
of large-scale motions due to rotation, infall, or expansion. We find that the
clump splits into six distinct cores when observed at sub-arcsecond resolution.
These are identified through their 1.4 mm continuum and molecular line
emission. We produce maps of the velocity, line width, and rotational
temperature from the methanol and methyl cyanide lines, which allow us to
investigate the cores and reveal a velocity and temperature gradient in the
most massive core. We also find evidence of a bipolar outflow, possibly powered
by a low-mass star. We present the tentative detection of a circumstellar
self-gravitating disk lying in the most massive core and powering a large-scale
outflow previously known in the literature. In our scenario, the star powering
the flow is responsible for most of the luminosity of IRAS23385+6053
(~$3000~L_\odot$). The other cores, albeit with masses below the corresponding
virial masses, appear to be accreting material from their molecular
surroundings and are possibly collapsing or on the verge of collapse. We
conclude that we are observing a sample of star-forming cores that is bound to
turn into a cluster of massive stars.
