COMBINE 8 cups water and cinnamon in large saucepan. Bring to a boil.
PLACE remaining water and flour in blender; cover. Blend until smooth. Pour mixture through fine mesh sieve into cinnamon-water mixture. Bring to a boil. Reduce heat to low; cook, stirring constantly with wire whisk, for 6 to 7 minutes or until mixture is thickened.
STIR in sugar, chocolate and vanilla extract. Cook, stirring frequently, for 4 to 5 minutes or until chocolate is melted and flavors are blended. Remove cinnamon sticks. Pour into mugs.