Add all the ingredients to a shaker and fill with ice.
Shake, and double-strain into a coupe glass.
Garnish with a pickled rhubarb stalk.
*Spiced Rhubarb Shrub
2 tbsp Coriander seeds
3 tbsp Pink peppercorns
4 cups Sugar
1 qt (32 oz) Raspberry vinegar
4 cups Chopped rhubarb
Toast the coriander and peppercorns for a minute or two in a saucepan over medium heat. Add the remaining ingredients and cook just until it begins to bubble. (The sugar will dissolve, and the rhubarb will begins to break down.) Remove from the heat and let cool completely. Strain through a sieve, pressing the rhubarb to extract as much liquid as possible.
**To make Pickled Rhubarb, pour cold Spiced Rhubarb Shrub over fresh rhubarb stalks trimmed and chopped into 3-inch pieces. Refrigerate for at least a few hours before using. This cocktail is served at The Thomas in Napa, Calif.