Spiced Tamarind Buck

Prepare tamarind puree by softening a small piece of brick tamarind in enough hot water for a few minutes, then straining out seeds and fibres. Use the listed 0.5 oz prepared puree portion. Muddle 2 of the 3 listed mint sprigs with falernum and orange liqueur. Add the rum, lime juice, tamarind puree, exactly 2 dashes spice bitters and ice, then shake. Strain over one large ice cube, top with the listed 55 cc ginger beer and 55 cc soda water and finish with the remaining mint sprig.