Peel the cucumber, cut into thin slices, season with salt and set aside. Peel and finely dice the shallots.
Heat the oil in the saucepan and sauté shallots in it until translucent. Add the veal stock, vinegar, salt, pepper and sugar and bring to the boil. Pour the vinegar stock through a sieve into a saucepan, squeeze out the residue in the sieve well. Boil the potatoes as jacket potatoes, drain, steam, peel as warm as possible. Beat the egg yolks with the whisk over a mild heat under the vinegar stock until it has a slightly creamy consistency.
Cut the warm potatoes into the egg yolk sauce and carefully fold in. Cover the lettuce aside and let it steep a little. In the meantime, dice the eel fillet, fry briefly without fat and allow to drain on kitchen paper. Do not chop the dill boxes too finely. Sprinkle eel and dill on top of the salad before serving.