A shrub syrup is a delicious, vintage-style syrup made with fruit, sugar, and a form of acid (in this case, vinegar). You can make shrubs with everything from blackberries to oranges.
Finely mince the apples and set aside. Heat the sugar and water in a saucepan over medium-low heat, stirring occasionally, until the sugar dissolves. Add the fruit, reduce heat to low, and stir for 5 minutes. Allow the mixture cool, add vinegar to the syrup, pour it into a mason jar, and store the mixture in the refrigerator for three days, shaking occasionally. Strain the solids and the shrub is ready to use, although it will age well in the fridge.