Remove the skin from the eel fillets, making sure not to lose too much of the jelly between the flesh and skin as there is lots of flavour in this, then slice it thickly.
Slice the celery hearts lengthways, then wash and thinly slice. Keep the pale leaves.
Measure the lemon juice, then mix it with 3 times its volume of extra-virgin olive oil. Season with sea salt and freshly ground black pepper and crumble in the dried chillies.
Put the capers in a small bowl and add 1 tablespoon of the olive oil dressing.
In a separate bowl, mix the celery and leaves with the remaining dressing. Add horseradish cream.
Divide the eel among 4 plates and scatter the celery, capers and anchovies, if using, over the top. Sprinkle with parsley, drizzle with horseradish cream and serve with lemon wedges to the side if desired.