AbstractPlasmonic metasurfaces tailored at the few‐nanometers scale and fabricated by high‐throughput lithography‐free methods are needed to efficiently produce optical components with optimal performance and small footprint. Herein, the design of such metasurfaces and their fabrication over cm2 areas by self‐assembly are reported. They present an optical cavity structure, in which a 2D array of parallel Au nanorods is coupled to a metal mirror through a thin spacer. The nanorods present a quasi‐monodisperse ≈10 nm diameter and separation, and a broad polydisperse length distribution. These remarkable nanostructural features, combining periodicity in one direction with randomness in another, endow the nanorod array with unconventional plasmonic and anisotropic effective optical properties. Thanks to these properties, for light polarized along the nanorods, the metasurface displays strong destructive optical interference and thus near‐perfect absorption over a broad range of angles of incidence and of wavelengths in the near infrared. In contrast, for light polarized perpendicular to the nanorods, no such interference occurs and thus the metasurface behaves as a metal mirror. In sum, the metasurface can be used as broadband omnidirectional polarizing mirror, an original thin and monolithic optical component merging the functionalities of a metal mirror and of a wire‐grid polarizer.