Cook Blueberries - In a medium saucepan, bring blueberries and water to a boil. Reduce heat to medium and cook until berries begin to burst, about 12 minutes. Stir occasionally.
Warm Version - Strain over a bowl and then gently press berries to extract all their juice into the bowl. Discard berries and return liquid to saucepan. Add sugar, cinnamon stick, lemon zest and juice. Bring saucepan to a boil. Add cornstarch slurry to pot and cook, while stirring, until soup is thick, about 3-5 minutes. Discard cinnamon and serve warm with whipped cream.
Cold Version - Make as in the hot version but straining is optional. Continue with recipe and after cornstarch slurry has been cooked, remove pot from heat and let cool to room temperature. Store in refrigerator to cool completely. Before serving, combine whipped cream, sour cream, sugar, and vanilla. Serve the cold blueberry soup with a dollop of the cream on top.