The Italian name for this savoury cake is 'Scarpaccia viareggina salata' and it originates from Tuscany. As the name suggests, this cake has to be flat as a shoe (scarpa in Italian), and therefore perfectly crisp.
The secret for a great scarpaccia is to have a flat and crisp cake. Therefore, pick a large baking tin or dish and spread the mix all over. This way, the scarpaccia will be "al suolo" as Tuscans say, meaning literally "on the ground" or really flat.