Step #1 lemon peel, thinly sliced (yellow part only) fresh lemon balm or mint sprigs SAUCE: mix 4 c fresh blueberries (or frozen), water, lemon juice & cornstarch in heavy large saucepan.
Step #2 Stir over medium-high heat until mixture boils & thickens.
Step #3 Cool slightly.
Step #4 Puree mixture in processor or mixer until smooth.
Step #5 Mix in sugar.
Step #6 put in the fridge until chilled, about 3 hrs.