The availability of robust, scalable and automated nanoparticle manufacturing processes is crucial for the viability of emerging nanotechnologies. Metallic nanoparticles of diverse shape and composition are commonly manufactured by solution-phase colloidal chemistry methods, where rapid reaction kinetics and physical processes such as mixing are inextricably coupled, and scale-up often poses insurmountable problems. Here we show how self-assembly of ordered microscale foams enables a simple yet general solution for remarkably precise, scalable and automated nanoparticle synthesis. We demonstrate this by presenting the first continuous process to synthesize thin gold 'nanoshells' and 'nano-islands' on silica nanoparticle surfaces.