Preparation - Drain the thawed raspberries, one box at a time. Leave one box of raspberries whole; set aside. Puree the other raspberries... crush and strain the berries in a food mill or puree in a food processor and strain to remove the seeds. Pour the puree into a small saucepan. Mix the water, lemon juice and cornstarch together in a cup or small bowl. Add the mixture to raspberry puree in the saucepan. Bring to full boil over medium high heat, stirring constantly. Remove from heat. Let cool slightly before stirring in the whole reserved whole raspberries. Serve warm or chilled over ice cream and other desserts.