Blackberry Shrub:Combine the blackberries and sugar in a covered bowl, ensuring the berries are evenly coated. Let macerate at room temperature for 6 hours. Add the balsamic vinegar and water, then blend until smooth. Strain through a fine mesh strainer. Refrigerate for up to 3 weeks.
To prepare a cocktail, blend bourbon and frozen peach lemonade with ice until smooth. Pour into a Collins glass. Add 2 dashes of bitters and stir gently. Finish with a blackberry shrub floater.