1: In a bowl, combine flat-leaf parsley, onion, capers, Dijon mustard, lemon juice, mayonnaise, and Worcestershire sauce.
2: Mix well until all ingredients are blended together.
3: Season with black pepper and add distilled white vinegar.
4: Incorporate cornichon juice or dill pickle juice into the mixture.
5: Finally, fold in coarsely chopped cornichons or dill pickles.
6: Serve with fish and chips.
