The ability to harness light-matter interactions at the few-photon level plays a pivotal role in quantum technologies. Two-photon states are key quantum assets, but achieving them in individual emitters is challenging because their generation rate is much slower than competing one-photon processes. In this work, we show how atomically thin, finite-sized plasmonic nanostructures can harness two-photon spontaneous emission (TPSE) resulting in giant production of hyper-entangled photon-photon, plasmon-plasmon, and hybrid photon-plasmon states, far beyond what is feasible with extended monolayers or 3D geometries. We unravel these TPSE channels and show how their distinct Fano and Lorentzian spectral line-shapes provide a fingerprint to resolve photon-photon and photon-plasmon pathways via standard far-field single-photon spectroscopy measurements. We further show customization of the emitted two-quanta spectrum by actively tailoring the nanostructures’ optical response. We demonstrate that single photon generation via two-quanta photonic transitions can be orders of magnitude more efficient than standard one-photon spontaneous emission due to the high amplification of the photon-plasmon decay channel offered by the dark-modes supported in the nanostructure. The enormous field confinement of our ultrathin nanostructures also severely impacts the usual unbalance between one- and two-quanta emission rates, allowing the latter to be competitive with the former.