In each of two large stockpots, combine 2-1/2 cups cocoa, 1-1/2 cups sugar and 1 teaspoon salt. Gradually stir 5 cups water into each pot. Bring to a boil; reduce heat. Whisk in the milk, cream and remaining water; heat through. Remove from the heat; stir in vanilla. Garnish with whipped cream and additional cocoa.