Add the Rhubarb Simple Syrup, white rum, lime juice, ginger, aged rum and pomegranate juice to a mixing glass. Muddle the ginger, add large ice and shake thoroughly in a cocktail shaker. Double-strain into a rocks glass with fresh ice, garnish with a rhubarb stalk and serve.
Add the rhubarb and 2 cups water to a small pot and bring to a boil. Reduce to a simmer and add the sugar. Stir until dissolved, then take off the heat. Let steep for 10 minutes, then strain and let cool. Store in the refrigerator for up to 2 weeks.