Rinse berries and drain dry on absorbent towels. In a 1-1/2 quart pan, combine sugar and cornstarch. Add 1 cup of the berries and the water. Cook, stirring often, over medium-high heat until mixture comes to a full boil, 5 to 7 minutes.

Distribute nectaries and remaining berries in an even layer in pastry; spoon hot berry mixture over fruit. Chill until glaze is set.