  We present VLA observations toward the Class 0 protostar L1157 MMS at 6.8 mm
and 9 mm with a resolution of ~0.04" (14 au). We detect two sources within
L1157 MMS and interpret these sources as a binary protostar with a separation
of ~16 au. The material directly surrounding the binary system within the inner
50 au radius of the system has an estimated mass of 0.11 M_sun, calculated from
the observed dust emission. We interpret the observed binary system in the
context of previous observations of its flattened envelope structure, low rates
of envelope rotation from 5000 to 200 au scales, and an ordered, poloidal
magnetic field aligned with the outflow. Thus, L1157 MMS is a prototype system
for magnetically-regulated collapse and the presence of a compact binary within
L1157 MMS demonstrates that multiple star formation can still occur within
envelopes that likely have dynamically important magnetic fields.
