Simple and quick techniques for assembling nanoparticles in topographically designed Poly(dimethylsiloxane) moulds of nanosized shapes have great potential in many spectroscopic and sensing tools. Close-packed particles pose rich plasmonic resonances, enabling the optical response to be tailored on both the nano- and macroscale. Template-assisted self-assembly (TASA) is a method that creates colloidal aggregates with controlled sizes formed by dewetting aqueous dispersions of NPs across surfaces. We present rapid TASA (rTASA), a modified version with an overall process time of under 10 min, improving speed and user-friendliness. Depending on the array pitch distance and average number of NPs per trap, the transmission through the template drops by between 20 and 80%, enabling them to be detected with even the simplest spectroscopic solutions. This rapid method is useful as a building block to generate self-assembled systems that exhibit exciting optical properties in crucial areas, particularly in building a fast test for size-selective NP detection.