  Useful quantum metrology requires nonclassical states with a high particle
number and (close to) the optimal exploitation of the state's quantum
correlations. Unfortunately, the single-particle detection resolution demanded
by conventional protocols, such as spin squeezing via one-axis twisting, places
severe limits on the particle number. Additionally, the challenge of finding
optimal measurements (that saturate the quantum Cram{\'e}r-Rao bound) for an
arbitrary nonclassical state limits most metrological protocols to only
moderate levels of quantum enhancement. "Interaction-based readout" protocols
have been shown to allow optimal interferometry \emph{or} to provide robustness
against detection noise at the expense of optimality. In this Letter, we prove
that one has great flexibility in constructing an optimal protocol, thereby
allowing it to also be robust to detection noise. This requires the full
probability distribution of outcomes in an optimal measurement basis, which is
typically easily accessible and can be determined from specific criteria we
provide. Additionally, we quantify the robustness of several classes of
interaction-based readouts under realistic experimental constraints. We
determine that optimal \emph{and} robust quantum metrology is achievable in
current spin-squeezing experiments.
