This paper provides a comprehensive description of the design and commissioning of a dual-stage flow reactor for hydrothermal synthesis, notably heterogeneous nanomaterials such as core shell particles or nanocomposites. The design is based on the hypothesis that the next frontier of studies within continuous, hydrothermal synthesis lies as much with scalability as it does with the materials properties and performance in applications. Therefore, this reactor belongs to the up-scaled end of a laboratory system with a synthesis capacity of up to 50 g/h. Commissioning was accomplished with TiO2 nanoparticles as a model material. Results comply with earlier ones obtained from single-stage reactors. Dual-stage synthesis of a TiO2@SnO2 nanocomposite was performed by adding a SnCl4 solution to newly formed 9 nm TiO2 nanoparticles, yielding deposition of 2 nm rutile SnO2. Synthesis of pure SnO2 produced much larger nanocrystals, indicating that TiO2 nanoparticles provide the nucleation sites for SnO2 and impede the growth beyond 2 nm.