In a small bowl, dissolve the Granulated Sugar in warm Water — about 1/4 cup sugar into 1/2 cup warm water is a good starting point — stirring until fully dissolved to make a light syrup.
Let the syrup cool slightly, then stir in equal parts Fish Sauce and Lime Juice; a good initial ratio is about 2–3 tablespoons of each for the syrup above, but you can adjust to taste.
Peel and finely mince the Garlic, and thinly slice or finely chop the Thai Bird's Eye Chili (remove seeds for less heat), then stir them into the sauce.
Taste and adjust: add more Lime Juice for tang, more Granulated Sugar to soften acidity, or more Fish Sauce for saltiness; if too strong, thin with a little extra Water.
Let the Nước Chấm rest at room temperature for 10–15 minutes so the flavors meld. Serve chilled or at room temperature alongside your dish.
