Put the carrot, celery, parsley, onion and a pinch of coarse salt in a saucepan (large enough to contain the meat as well) with enough cold water to cover the meat. Put the pan on the stove and bring the water to the boil. Now add the meat and leave to simmer for roughly an hour over a moderate heat (the meat must cook very slowly). In the meanwhile prepare the mayonnaise (1). Chop the tuna with the capers, gherkins and desalted and cleaned anchovies; delicately stir this mixture and the juice of the lemon into the mayonnaise. When the meat is cooked, lay it on a chopping board to cool with a light weight on top of it. When it is cold, slice it thinly with a sharp knife and arrange the slices, in a single layer, on a serving dish. Cover with the tuna sauce and garnish with slices of carrot, either raw or briefly blanched, and with a few capers. Leave the “vitello tonnato” in the fridge for a few hours, covered with cling film, so that it gains flavour.
This dish has many advantages: it can be prepared in advance, even the day before (it’ll be even tastier); leftover meat, both roast and boiled, can be “recycled” (with excellent results!) by slicing it thinly and dressing it with the sauce, following the recipe – it’s delicious! Another tip: if you like carpaccio (very thin slices of raw beef seasoned in various ways) you can “take advantage” of the tuna sauce as a dressing, it goes really well with it.