In a small bowl, whisk together mayonnaise, pickles, onion, and lemon juice. Season to taste with salt and pepper (I like 1/4 teaspoon salt and 1/8 teaspoon pepper). Cover and chill until serving time.
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Notes
Pickles: I love a crunchy dill pickle (Milwaukee's brand petite kosher dill pickles, if you can find them). Substitute sweet gherkins or pickle relish to taste, if you prefer that.
Lemon juice: Or substitute lime juice, vinegar, olive juice, or more pickle juice.
Yield: One batch of the recipe makes approximately 1 1/4 cups of tartar sauce.
Storage: Keep the sauce in the refrigerator until you're ready to eat.
Leftovers: Store any leftover sauce in an airtight container for up to 3 days in the refrigerator.
Make ahead: Can definitely be made a day or two before you need it (the flavors will have more time to blend).
Add-ins: It won't be classic, but it will still be delicious! Try minced fresh herbs like parsley, chives, or dill. Or try capers, chopped olives, sliced scallions, a squirt of mustard, or a dash of hot sauce.