  Supermassive black hole (BH) binaries are thought to produce self-lensing
flares (SLF) when the two BHs are aligned with the line-of-sight. If the binary
orbit is observed nearly edge-on, we find a distinct feature in the light curve
imprinted by the BH shadow from the lensed BH. We study this feature by
ray-tracing in a binary model and predict that 1\% of the current binary
candidates could show this feature. Our BH tomography method proposed here
could make it possible to extract BH shadows that are spatially unresolvable by
high-resolution VLBI.
