Our setup allows the Weibel instability and its interplay with the Biermann battery to be probed in laser-driven collisionless plasmas. Ab initio particle-in-cell simulations of the interaction of short (
≤
1
ps
) intense
(
a
0
≥
1
)
laser pulses with overdense plasma targets show observable Weibel generated magnetic fields. This field strength surpasses that of the Biermann battery, usually dominant in experiments, as long as the gradient scale length is much larger than the local electron inertial length; this is achievable by carefully setting the appropriate gradients in the front of the target, e.g., by tuning the delay between the main laser pulse and the prepulse.