Baccalà con i porri belongs on Emilia-Romagna’s PAT gastronomy register, where the same dish is also entered as E’ bacalà con i por. That listing is why the pairing of salt cod and leek deserves a closer look: it is not a vague regional rumour but a named preparation with an official place on the map.
In the Forlì-Cesena method the pan does the storytelling. Pieces of salt cod take colour first. Chopped leek then goes into that same vessel with tomato, picking up the fond before the fish returns so the two strands finish together rather than in separate pots.
The useful cue is sequence, not a full kitchen script: brown the baccalà, then let leek and tomato work in the identical pan, then reunite. Anyone tracing Emilia-Romagna PAT names can treat Forlì-Cesena as the documented home of that order, and look next at neighbouring listed fish dishes that share the same register.