1. Add all ingredients to a cocktail shaker with ice and shake vigorously. Pour into 2 stemmed or ‘up’ glasses. Rim each glass with a lime triangle you’ve sliced and leave the lime on the rim.

For the Plum Shrub

1. Combine the plums and sugar, giving it a good stir to coat the plums, and store in the refrigerator for 2 days, covered. (Feel free to use the very jar you plan to store the shrub in when it’s complete.) Pour the contents into a colander and reserve the liquid, but mush it about (with the back of a spoon or a muddler) to get the fruit to express its juice. Into that juice add the 2 vinegars.
2. Pour that into what will no doubt be a very full quart Mason jar and put it back into the fridge, taking it out every day or so to give it a good shake. After a week, taste it. It should be on a f ine point of sweet-sour. If you’re happy with it, start making the cocktail, and if not, wait. It only deepens in flavor over time, and if kept sealed and refrigerated should last pretty much forever, if you don’t use it up in a month.