Fill a pitcher with the ice, then add the bourbon, lemon juice, mint and Rhubarb Simple Syrup, and stir to combine. Top with the ginger beer, and serve in glasses with a mint sprig garnish
Rhubarb Simple Syrup:
Place the rhubarb, sugar and 1 cup water in a medium saucepan set over medium-high heat. Bring to a boil and cook until the sugar dissolves and the rhubarb softens, 5 to 8 minutes. Transfer to a blender and puree until smooth. Yield: 2 1/2 cups.
Substitute the bourbon and ginger beer with ginger ale for a non-alcoholic version of this drink.
When blending hot liquid, first let it cool for five minutes or so, then transfer it to a blender, filling only halfway. Put the lid on, leaving one corner open. Cover the lid with a kitchen towel to catch splatters, and pulse until smooth.