Debone herrings. Drain beet. Peel eggs and potatoes. Peel apple, quarter, core. Peel onion.
Peel celery. Dice everything, as well as the roast pork.
For the vinaigrette, mix oil, vinegar, water and mustard, season with pepper, sugar and salt. Mix with the salad ingredients, mix well, season the lettuce again if necessary. If it is too dry, add a little more hot water.