  We report the discovery of a white dwarf exhibiting deep, irregularly shaped
transits, indicative of circumstellar planetary debris. Using Zwicky Transient
Facility DR2 photometry of ZTF$\,$J013906.17+524536.89 and follow-up
observations from the Las Cumbres Observatory, we identify multiple transit
events that recur every ${\approx}\,107.2\,$d, much longer than the
$4.5{-}4.9\,$h orbital periods observed in WD$\,$1145+017, the only other white
dwarf known with transiting planetary debris. The transits vary in both depth
and duration, lasting $15{-}25\,$d and reaching $20{-}45\,\%$ dips in flux.
Optical spectra reveal strong Balmer lines, identifying the white dwarf as a DA
with $T_{\mathrm{eff}}=10{,}530\pm140\,\mathrm{K}$ and $\log(g)=7.86\pm0.06$. A
$\mathrm{Ca\,II\,K}$ absorption feature is present in all spectra both in and
out of transit. Spectra obtained during one night at roughly $15\,\%$ transit
depth show increased $\mathrm{Ca\,II\,K}$ absorption with a model atmospheric
fit suggesting $[\mathrm{Ca/H}]=-4.6\pm0.3$, whereas spectra taken on three
nights out of transit have $[\mathrm{Ca/H}]$ of -5.5, -5.3, and -4.9 with
similar uncertainties. While the $\mathrm{Ca\,II\,K}$ line strength varies by
only 2-sigma, we consider a predominantly interstellar origin for Ca absorption
unlikely. We suggest a larger column density of circumstellar metallic gas
along the line of site or increased accretion of material onto the white
dwarf's surface are responsible for the Ca absorption, but further
spectroscopic studies are required. In addition, high-speed time series
photometry out of transit reveals variability with periods of 900 and
1030$\,$s, consistent with ZZ Ceti pulsations.
