Prepare the remoulade sauce. Divide the egg into yolk and white. Finely chop the protein. Rub the yolk with a small amount of mayonnaise, stir in the remaining mayonnaise. Finely chop the capers and garlic. Mix mayonnaise with capers, garlic, parsley, tarragon and mustard.
Peel the celeriac and cut into 6mm thick slices. Boil in boiling salted water for 3-4 minutes. Drain the water, cool the celery. Cut into thin strips and season with remoulade sauce. Arrange in salad bowls, sprinkle with herbs.