  Using blazar light curves from the optical All-Sky Automated Survey for
Supernovae (ASAS-SN) and the $\gamma$-ray \textit{Fermi}-LAT telescope, we
performed the most extensive statistical correlation study between both bands,
using a sample of 1,180 blazars. This is almost an order of magnitude larger
than other recent studies. Blazars represent more than 98\% of the AGNs
detected by \textit{Fermi}-LAT and are the brightest $\gamma$-ray sources in
the extragalactic sky. They are essential for studying the physical properties
of astrophysical jets from central black holes. However, their $\gamma$-ray
flare mechanism is not fully understood. Multi-wavelength correlations help
constrain the dominant mechanisms of blazar variability. We search for temporal
relationships between optical and $\gamma$-ray bands. Using a Bayesian Block
Decomposition, we detect 1414 optical and 510 $\gamma$-ray flares, we find a
strong correlation between both bands. Among all the flares, we find 321
correlated flares from 133 blazars, and derive an average rest-frame time delay
of only 1.1$_{-8.5}^{+7.1}$ days, with no difference between the flat-spectrum
radio quasars, BL Lacertae-like objects or low, intermediate, and
high-synchrotron peaked blazar classes. Our time-delay limit rules out the
hadronic proton-synchrotron model as the driver for non-orphan flares and
suggests a leptonic single-zone model. Limiting our search to well-defined
light curves and removing 976 potential but unclear ``orphan'' flares, we find
191 (13\%) and 115 (22\%) clear ``orphan'' optical and $\gamma$-ray flares. The
presence of ``orphan'' flares in both bands challenges the standard one-zone
blazar flare leptonic model and suggests multi-zone synchrotron sites or a
hadronic model for some blazars.
