For the lamb’s tongue, bring a large saucepan of water to the boil, add the tongue and your vegetables, then return to a simmer and cook for 2½–3 hours. Remove from the heat and let the tongue cool in the water. Lift the tongue out of the water, peel it and cut it in half lengthways. Strain and reserve the stock.
Rub the lamb loin lightly with the oil and season well with salt and pepper. Preheat a griddle pan over a high heat and griddle the lamb for 8–10 minutes, or until cooked, turning regularly. Leave to rest for 5 minutes.
Meanwhile, heat half the butter in a small frying pan. Add the kidney and sauté for 3–4 minutes on each side, or until cooked. Remove and set aside to rest.
Heat the remaining butter in a heavy-based saucepan and sauté the cooked tongue cut side-down for 3–4 minutes, until coloured and hot through. Set aside to rest.
For the coriander sauce, purée all the ingredients together with a pinch of salt and pepper in a food processor. Start with 100ml/3½fl oz oil and increase if needed.
For the coriander salad, mix the celery, shallot and coriander together in a bowl. Combine the oil and vinegar in a small jar, then pour this over the salad and season well with salt and pepper.
To serve, slice the lamb loin. Put half the slices in each of two shallow bowls with a piece of tongue and kidney. Ladle over some the tongue stock and drizzle over a little coriander sauce. Serve with the salad.