1 quart (4 cups) vanilla ice cream, slightly softened
1 teaspoon freshly grated lemon zest
2 tablespoons lemon juice
2 cups fresh blueberries
1/4 cup sugar
1/4 cup water
1 tablespoon cornstarch
Place ice cream in large bowl; add lemon zest and lemon juice; mix well.
Cover; freeze until firm (3 to 4 hours).
Combine all sauce ingredients in 2-quart saucepan; mix well.
Cook over medium heat, stirring constantly, until mixture boils and thickens (5 to 7 minutes). Cool completely.
To serve, spoon sauce over ice cream.