  We report on exceptionally bright bursts (>400 Jy ms) detected from the
repeating fast radio burst source FRB 20220912A using the Nan\c{c}ay Radio
Telescope (NRT), as part of the ECLAT (Extragalactic Coherent Light from
Astrophysical Transients) monitoring campaign. These bursts exhibit extremely
luminous, broadband, short-duration structures (~ 16 microseconds), which we
term 'microshots' and which can be especially well studied in the NRT data
given the excellent signal-to-noise and dynamic range (32-bit samples). The
estimated peak flux density of the brightest microshot is 450 Jy. We show that
the microshots are clustered into dense 'forests', by modelling them as Weibull
distributions and obtaining Weibull shape parameters of approximately 0.5. Our
polarimetric analysis reveals that the bursts are nearly 100% linearly
polarised; have < 10% circular polarisation fractions; a near-zero average
rotation measure of 0.10(6) rad/m^2; and varying polarisation position angles
over the burst duration. For one of the bursts, we analyse raw voltage data
from simultaneous observations with the Westerbork RT-1 single 25-m dish. These
data allow us to measure the scintillation bandwidth, 0.30(3) MHz, and to probe
the bursts on (sub-)microsecond timescales. Some important nuances related to
dedispersion are also discussed. We propose that the emission mechanism for the
broadband microshots is potentially different from the emission mechanism of
the broader burst components which still show a residual drift of a few hundred
MHz/ms after correcting for dispersion using the microshots. We discuss how the
observed emission is phenomenologically analogous to different types of radio
bursts from the Sun.
