COMBINE milk, cream, rice and sugar in large saucepan (or medium saucepan for trial recipe). Cook on medium-low heat 30 min. or until rice is tender, but not mushy, stirring occasionally. (Watch carefully so rice mixture does not boil over.)
ADD chocolate and vanilla; cook until chocolate is completely melted, stirring constantly. Remove from heat. Stir in OREO Pieces.
LADLE 2/3 cup of the rice mixture into each of 50 small dessert dishes (or 7 dessert dishes for trial recipe). Cover and refrigerate at least 4 hours before serving.