Combine mayonnaise, dill pickles, and fresh lemon juice in a medium-sized bowl.
Mix well until the ingredients are fully integrated.
Add parsley, sugar, and black pepper to the bowl.
Stir the mixture thoroughly, ensuring an even distribution of all components.
Incorporate the finely chopped onion into your sauce if you chose to use this optional ingredient.
Mix to combine once more.
Allow the mixture to rest in the refrigerator.
Chill for at least one hour to let the flavors blend together.
Taste the sauce and adjust seasonings if needed.
You might want to add more lemon juice or pepper based on personal preference.