Vary with whatever fruit is in season and economical!
Combine corn starch and sugar in a small microwave-safe bowl. Gradually add juices until well blended. Add water and butter.
Microwave on HIGH (100%) power for 3 minutes, stirring after each minute. Continue to microwave another 60 to 90 seconds, stirring every 30 seconds until mixture thickens and boils.
Cool at least 30 minutes. Pour over fruit. Chill 30 minutes before serving.