-halved and sectioned In a large bowl, combine strawberries, blueberries and blackberries and half cup sugar. Let stand at room temperature until the berries thaw, about 1.5 hours. Stir occasionally, taste, adding the remaining sugar if necessary. In a large colander, strain the berries with a bowl under it so you can save the juice. Place the cornstarch in a medium saucepan and stir in the juice. Turn on the heat to medium and cook, stirring, until the juice becomes thick and translucent, about 10 to 15 minutes. Let it cool. Place the berries in an attractive bowl. Pour the sauce over the fruit. Add the oranges and stir gently. Cover and chill until serving time.