From David Lebovitz
Garnish: peach slices, fresh mint
Put the peach pieces in a cocktail shaker with the muscovado syrup. Use a muddler or a fork to mash them very well, so they are liquified as much as possible.
Add the bourbon and Bonal to the cocktail shaker. Fill the shaker half-full of ice, cover and shake vigorously until well-chilled and the ice is broken up, 15 to 20 seconds.
Double strain into a tumbler, then add ice. Top with a splash of ginger beer or other sparkler. Garnish with peach slices and fresh mint.
To make muscovado syrup: (1) heat ¼ cup (60ml) water with ¼ cup (50g) dark brown sugar; (2) stir over the heat until the sugar is completely dissolved; (3) remove from heat and let cool, then pour into a jar and refrigerate until ready to use. The syrup will keep for at least a week. If you can't get Bonal, substitute crème de pêche (or peach liqueur), Lillet, Cap Corse, Dubonnet, or a red vermouth that leans toward the bitter side. If using something on the sweet side, like crème de pêche or Lillet, you may want to use only ¼ ounce of the muscovado syrup.