Bring first 5 ingredients to a boil in a saucepan over medium-high heat, stirring often. Remove from heat and cool slightly.
Process cooled blueberry mixture with lemon juice in a blender or food processor until smooth, stopping to scrape down sides. Cover and chill until ready to serve.
Stir in half and half just before serving. Serve in stemmed glasses. Garnish with sliced mint. For a creamier soup, add a dollop of plain yogurt to each serving.
Crystal’s Tips:
Blackberries may be used instead of blueberries.
Leftover soup makes great ice cream! (I’m definitely going to try that!)