  One major goal in fast radio burst science is to detect fast radio bursts
(FRBs) over a wide field of view without sacrificing the angular resolution
required to pinpoint them to their host galaxies. Wide-field detection and
localization capabilities have already been demonstrated using
connected-element interferometry; the CHIME/FRB Outriggers project will push
this further using widefield cylindrical telescopes as widefield outriggers for
very long baseline interferometry (VLBI). This paper describes an offline VLBI
software correlator written in Python for the CHIME/FRB Outriggers project. It
includes features well-suited to modern widefield instruments like
multibeaming/multiple phase center correlation, pulse gating including coherent
dedispersion, and a novel correlation algorithm based on the quadratic
estimator formalism. This algorithm mitigates sensitivity loss which arises in
instruments where the windowing and channelization is done outside the VLBI
correlator at each station, which accounts for a 30 percent sensitivity drop
away from the phase center. Our correlation algorithm recovers this sensitivity
on both simulated and real data. As an end to end check of our software, we
have written a preliminary pipeline for VLBI calibration and single-pulse
localization, which we use in Lanman et al. (2024) to verify the astrometric
accuracy of the CHIME/FRB Outriggers array.
