Sprinkle gelatin over cold water in a small saucepan; let stand 1 minute. Cook over low heat, stirring until gelatin dissolves, about 2 minutes.
Combine gelatin mixture, buttermilk, sour cream, and sweetened condensed milk in a large bowl; stir until smooth. Pour mixture evenly into 6 (6-ounce) custard cups or ramekins. Cover and chill 1 hour or until set.
Combine blueberries and remaining ingredients in a medium saucepan; bring to a boil. Reduce heat, and simmer 3 to 4 minutes or until slightly thick. Cover and chill.
To serve, unmold custard cups onto individual dessert dishes. Top with blueberry sauce.