Current methods for performing microgrid black start require a series of steps to be performed where loads are connected and disconnected, making a fully-automated procedure unfeasible. This paper presents a novel method to perform a microgrid black start in a single step, enabling the procedure to be automatically carried out. Microgrids started in this way can then synchronise with each other and with the HV grid to expand the restored grid. The microgrid black start procedure is prepared during normal grid operation and requires only minimal communication in the microgrid to be executed during the blackout, relying on the DERs and storages in the microgrid being equipped with battery packs. Co-ordination in the multi-microgrid is performed with a multi-agent system. Inverter control algorithms are presented with results verifying the concept.