To make the mayonnaise, place all the ingredients, except the oil, into a food processor and blend until pale and creamy.
With the motor running, pour in enough oil, in a steady stream, until the mayonnaise is thick.
For the Remoulade, place the celeriac, lemon juice, mustard, seasoning and parsley into a large bowl.
Mix together well and stir in the home-made mayonnaise. Season to taste.
Mix to combine and serve.
