In a saucepan, combine the blueberries, water, sugar and salt; cook and stir over low heat until sugar is dissolved. Bring to a boil. Reduce heat; simmer, uncovered, for 7 minutes or until the berries burst.
Combine cornstarch and cold water until smooth; stir into hot blueberry mixture. Bring to a boil; cook and stir for 2 minutes or until thickened. Remove from the heat; stir in the lemon juice, vanilla and cinnamon. Serve over ice cream.
If using frozen blueberries, use without thawing to avoid discoloring the batter.