  Post-common-envelope binaries (PCEBs) containing a white dwarf (WD) and a
main-sequence (MS) star can constrain the physics of common envelope evolution
and calibrate binary evolution models. Most PCEBs studied to date have short
orbital periods ($P_{\rm orb} \lesssim 1\,$d), implying relatively inefficient
harnessing of binaries' orbital energy for envelope expulsion. Here, we present
follow-up observations of five binaries from {\it Gaia} DR3 containing
solar-type MS stars and probable ultramassive WDs ($M\gtrsim 1.2\,M_{\odot}$)
with significantly wider orbits than previously known PCEBs, $P_{\rm orb} =
18-49\,$d. The WD masses are much higher than expected for systems formed via
stable mass transfer at these periods, and their near-circular orbits suggest
partial tidal circularization when the WD progenitors were giants. These
properties strongly suggest that the binaries are PCEBs. Forming PCEBs at such
wide separations requires highly efficient envelope ejection, and we find that
the observed periods can only be explained if a significant fraction of the
energy released when the envelope recombines goes into ejecting it. Our 1D
stellar models including recombination energy confirm prior predictions that a
wide range of PCEB orbital periods, extending up to months or years, can
potentially result from Roche lobe overflow of a luminous AGB star. This
evolutionary scenario may also explain the formation of several wide WD+MS
binaries discovered via self-lensing, as well as a significant fraction of
post-AGB binaries and barium stars.
