In a medium saucepan, combine blueberries, water, and 3/4 cup sugar. Cook over medium heat until soup begins to thicken, about 8-10 minutes. Turn off the heat, add the vanilla bean and mint, and let steep for 30 minutes. Remove vanilla bean and scrape the seeds into the blueberry mixture; discard the bean pod and mint. Using a blender, process the mixture until smooth. Strain mixture through a fine mesh strainer into a picther or storage container; discard the solids. Cover and refrigerate soup.

While soup is cooking, mix creme fraiche with 1 tablespoon sugar and lemon and lime juice. Garnish soup with creme fraiche, cold heavy cream, or milk if desired.