In small saucepan, place sweet potato, cover with water and add 1/4 tsp. salt; cook until tender. In blender, put potato and enough potato cooking liquid to make smooth puree; set aside. In blender, puree beans with bean cooking liquid. Strain beans in fine-mesh strainer, pressing to extract all liquid. In large saucepan over medium-low heat, whisk potato, beans, milks, sugar, vanilla and 1/4 tsp. salt. Add cinnamon sticks, cloves and allspice. Simmer about 30 minutes, stirring occasionally to prevent sticking. Strain, discarding cinnamon, cloves and allspice. May be served warm or cold.