Combine blueberries, lemon peel, sugar, and water in a medium saucepan. Bring berry mixture to a boil over medium-high heat. Reduce heat to medium-low and simmer for 5 minutes. Strain the mixture through a fine mesh sieve, pressing on solids to release as much liquid as possible. Discard solids and return sauce to a clean saucepan. In a small bowl, combine the cornstarch and water, stirring until smooth. Add the cornstarch mixture to the blueberry sauce, stirring until the sauce comes to a boil. Allow to boil for 1 minute. Remove from the heat and cool sauce to room temperature. Serve with Lemony Panna Cotta.
Yield: 1 1/4 cups