You will need a 1-pint Mason jar with a tight-fitting lid for this recipe. Heating the jar with warm water and then draining it before adding the hot brine ensures that the jar won't crack from an abrupt temperature change.
Prick chiles with fork and set aside. Combine vinegar, sugar, salt, and peppercorns in small saucepan and bring to boil over medium-high heat.
Fill one 1-pint Mason jar with hot tap water to warm. Drain jar, then pack with chiles. Using ladle, pour hot brine over chiles to cover. Let cool to room temperature, about 30 minutes. Cover and refrigerate until flavors meld, about 24 hours. (Vinegar can be refrigerated for up to 3 months; flavor will continue to deepen over time.)
