Combine blueberries, sugar, and 1 & 1/2 cups of water in a medium-sized saucepan, over medium heat.
Cover with a lid and bring to a boil.
Adjust heat to low, then simmer for 10 to 15 minutes. Mix occasionally to ensure that nothing sticks at the bottom of the pan.
Take the pan off the heat and use an immersion blender to puree the softened blueberries.
In a separate small bowl, mix cornstarch with 1 tablespoon of cold water.
Place the pan back into the heat and slowly pour the cornstarch mixture while stirring.
Continue stirring your blueberry soup until it thickens, while adjusting the taste by adding more sugar, if preferred.
Remove the pan from the heat and transfer it into serving bowls.
Place a dollop of whipped cream on top of each serving of blueberry soup, then serve.