How to Make It
Stir together 1/2 cup water, lime juice, and sugar in a small bowl until sugar dissolves. Add additional lime juice and/or sugar to taste; dilute with water if flavors are too strong. If there’s an unpleasant tart-bitter edge, add rice vinegar to fix flavor.
Stir in fish sauce; add additional fish sauce to taste. (How much you use depends on the brand and your own taste.) Aim for a bold, forward finish that’s a little gutsy. Keep in mind that this sauce typically dresses dishes that include unsalted ingredients such as lettuce and herbs, which will need an extra flavor lift.
If using, stir in carrot, chile, and/or garlic. (Offer chile on the side if diners are sensitive to its heat.) Serve sauce in a bowl on the table so diners may help themselves, or divide among small individual bowls in advance.
VARIATIONS: For a vegetarian nuoc cham: Stir together 3 tablespoons light brown sugar (or 4 to 5 tablespoons pure maple syrup), 3 tablespoons fresh lime juice, and a rounded 1/2 teasopon finely ground sea salt in a small bowl until sugar dissolves. Taste and add additional sugar or up to 1 teaspoon rice vinegar to round out the lime juice. Stir in 2/3 cup lukewarm water and 1 1/2 teaspoons soy sauce. Finish with any add-ins before serving.