- 1 cup sugar
- 1/4 cup unseasoned rice vinegar
- 10 ounces fresh or frozen blackberries (about 2 cups)
- Cook sugar in a medium saucepan over medium heat, without stirring, until it begins to turn golden brown around the edges. Stir to incorporate melted sugar and cook, stirring occasionally, until all sugar is melted and caramel turns a deep amber color, 6–8 minutes.
- Remove pan from heat and carefully add vinegar to caramel (mixture will bubble vigorously and seize), then add berries. Return pan to medium heat and cook, stirring occasionally, until seized caramel is melted and berries are softened, 6–8 minutes. Let cool.
- DO AHEAD: Caramel sauce can be made 1 week ahead. Cover and chill.