The generation and control of heat transport with nanoparticles is an essential objective of thermoplasmonics. Janus nanoparticles consisting of dissimilar materials with contrasting interfacial Kapitza conductance provide a route to control heat transport at the nanoscale. Here we use the recently introduced Atomistic Nodal Approach to map the surface temperature and Kapitza conductance of Janus nanoparticles to individual atoms. We show that the transition in the thermal transport properties between the hydrophobic and hydrophilic interfaces is exceptionally abrupt, occurring over length scales below 1 nm. We demonstrate the generality of this result using coarse-grained and all-atom models of gold nanoparticles. Further, we show how this behaviour provides a route to sustain significant temperature differences, on the order of tens of degrees for μW heat rates, between adjacent molecular layers attached to heated gold nanoparticles. Our work provides fundamental insight into nanoscale heat transport and a principle to design heterogeneous Janus nanoparticles for thermal transport applications.