In this work, we theoretically investigate a tandem crossed twisted nematic liquid crystal architecture for the generation of broadband (“white”) optical vortices. Operating in transmission, the system consists of two twisted nematic cells cascaded such that the liquid crystal director at the output of the first cell is strictly orthogonal to the director at the input of the second. Unlike conventional q-plates, this crossed configuration preserves the handedness of incident circularly polarized light. By rotating the entire polarization state by a target angle, the architecture imparts a corresponding spatial phase shift directly to the circular polarization. To evaluate its performance under realistic physical conditions, we develop a rigorous Jones matrix model. We systematically analyze the impact of deviations from the ideal waveguiding regime, manufacturing thickness mismatches, oblique incidence, and structural misalignments. By utilizing the modal overlap integral, we establish strict analytical figures of merit that provide a universal lower bound for the global mode purity. To mitigate the inherent amplitude and phase distortions, we propose three distinct operational strategies, ranging from parameter optimization to active phase correction. We demonstrate that active compensation effectively decouples the amplitude transmission efficiency from fabrication thickness tolerances, ensuring high optical throughput and superior phase fidelity. Ultimately, the direct structural compatibility of this architecture with emerging in-plane switching technologies establishes the tandem twisted nematic cell as a highly versatile blueprint for next-generation, fully dynamic broadband spatial light modulators.