The hero of this dish is the ragout of leeks. I have put the fish in pastry to keep it stress-free, but you can also serve the ragout alongside almost any poached, baked or pan-fried fish.
To make the chive oil, chop fresh chives very finely, bruise slightly with the side of a knife, scrape into a jar with the olive oil and season well with salt and pepper.
For the ragout, remove the coarse, green ends of the leeks.
Cut them lengthways and shred finely. Put into a sieve and wash well under cold, running water to remove any soil or sand.