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We demonstrate a unique combination of capabilities involving (1) electron-beam lithography at sub-5-nm length scales on ultrathin membranes, (2) electron energy-loss spectroscopy (EELS) down to 0.3 eV, and (3) full electromagnetic simulation of plasmon excitation by electrons to uncover the phenomena occurring when two nanoprisms are brought closer than 1 nm. The smallest dimensions of structures as investigated by EELS and imaged in a transmission electron microscope were of a 0.5 nm gap and a 3‑nm wide conductive bridge between these nanoprisms. The good agreement between our experimental results, electromagnetic calculations, and LC circuit models evidences the gradual evolution of the nanoprisms plasmonic resonances towards the quantum coupling regime.