1. With a vegetable peeler, pare off yellow peel from lemon and mince. Ream juice from lemon.
2. In a 5- to 6-quart pan, mix 3 tablespoons lemon juice (save extra for other uses), sugar, and cinnamon. Stir over high heat until mixture is boiling vigorously, 2 to 3 minutes. Remove from heat and stir in lemon peel and blueberries.
3. Serve warm or cool. Spoon into bowls and top with lemon verbena sabayon.