In a blender cover and blend the water and masa harina on medium until combined. Add both berries; cover and blend until smooth.
Press mixture through a medium-mesh sieve into a medium saucepan; discard seeds. Stir buttermilk into sieved mixture. Cook and stir over medium heat 25 minutes or until mixture starts to thicken. Reduce heat to medium-low; cook and stir 4 minutes more. Remove from heat. Stir in honey and vanilla.
To serve hot (traditional-style), ladle into cups and sprinkle with cinnamon. To serve cold, cool to room temperature. Return to blender and add 2 cups ice cubes. Cover and blend until smooth. Pour into tall glasses and sprinkle with cinnamon.