Place water, veal, carrot, celery, onion, olive oil, white wine vinegar and salt in a pot. Bring to the boil then simmer, covered, for about 2 hours or until veal is tender. Check every so often and top up with water if it necessary
To make the sauce: Hard boil the egg; remove shell and egg white. Place only the cooked egg yolk in a blender. Add tuna, anchovies, capers, olive oil and lemon juice; blend to a sauce.
Remove the veal from the pot and pat dry with kitchen roll. Slice and arrange the veal on a serving platter. Pour over tuna sauce; cover and refrigerate to allow the flavours to meld. Bring back to room temperature before serving. If you like, you can garnish with some sliced lemon and capers.