Peel the celeriac and cut into large pieces. Finely slice each piece on a mandolin and then cut into thin matchsticks. Roughly chop the parsley.
Place the egg yolks and mustard in a bowl and season with salt and pepper. Mix together and then slowly whisk in the oil. Once all of the oil has been incorporated, add the lemon juice.
Mix together the celeriac and the mayonnaise and sprinkle with chopped parsley to serve.
«Vary the type of mustard used in this mayonnaise to give a different flavour to your remoulade.»