Makes 2 cups
1/2 cup balsamic vinegar
2 cups ripe strawberries, stemmed, hulled, and roughly diced
2 tablespoons brown sugar
1/4 teaspoon kosher salt
1/8 teaspoon lemon zest
Bring balsamic vinegar to a boil in a small saucepan over medium heat. Reduce heat to low and simmer until vinegar has thickened and reduced to 1/4 of its original volume, 5 to 10 minutes.
Stir in strawberries, sugar, salt, and lemon zest. Increase heat to medium and bring to a boil. Reduce heat to low and simmer until strawberries have released their juices and softened, about 5 minutes.
With an immersion blender, puree slightly, or until smooth with a few pieces. Continue to simmer until sauce has thickened and is syrupy, 5 to 10 minutes more. Remove from heat, let cool to room temperature, then use immediately or transfer to an airtight container and store in refrigerator for up to a week.