This paper proposes to apply optimal approaches to the design and control of a highly constrained electric machine. The developed approach is applied on a permanent-magnet integrated starter generator (ISG) but may be applied on any high-constrained electric machine. One of the main problems in the use of optimal approaches is the accuracy of the models used by the optimizer. In our approach, we propose to proceed in two steps. 1) Optimal design: the model is purely analytic, and some phenomena are neglected (cross saturation). Under these conditions, the electric machine design is optimal for a limited number of constraints. The design model uses a classic uncoupled d,q reluctant circuit model (with saturation taken into account). 2) Optimal control: once the machine is calculated, the design constraints are validated by a finite-element (FE) method. The FE method allows to use a more accurate model to compute optimal currents for the control on the whole torque-speed plane. In our case, we use FE results to model the cross-saturation phenomenon. The optimizer is common to both cases and is a classic commercial sequential quadratic programming algorithm. This model is validated by experimental results based on an ISG. This paper shows that optimal design and control allows for permanent-magnet machine, high flux-weakening mode, and high-efficiency operations even for a simple machine structure