The aim of this proposal is to explore a potentially ubiquitous growth mechanism in colloidal nanoplatelets (NPL). Such nanoparticles are characterised by an atomically-defined thickness and display outstanding physical properties. Different growth mechanisms have been proposed to explain their controlled thickness, but they are still debated and no universal mechanism has been reported so far. Using time-resolved SAXS/WAXS for In2S3 NPL, we have identified an unreported growth mechanism based on a nucleation-induced lamellar self-assembly process. Our preliminary experiments on CeF3 and CdSe wurtzite NPL suggest a similar mechanism, hinting for a universal mechanism and begging further investigation. We propose to confirm these findings by broadening the range of experimental conditions on the anisotropic growth of different material to explore in detail their growth mechanism. This will advance our understanding of nanoparticle synthesis in general by setting up design rules.