  Results for the leading two-loop corrections of
$\mathcal{O}{\left(\alpha_t^2\right)}$ from the Yukawa sector to the
Higgs-boson mass spectrum of the MSSM with complex parameters are presented,
with details of the analytical calculation performed in the
Feynman-diagrammatic approach using a mixed
$\left.\text{on-shell}\middle/\,\overline{\text{DR}}\right.$ scheme that can be
directly matched onto the higher-order terms in the code ${\tt FeynHiggs}$.
Numerical results are shown for the masses and mixing effects in the neutral
Higgs-boson sector and their variation with the phases of the complex
parameters. Furthermore, the analytical expressions of the two-loop
self-energies and the required renormalization constants are recorded. The new
results can consistently be implemented in ${\tt FeynHiggs}$.
