Melt chocolate chips; stirring until smooth. In a separate bowl, combine the milk, egg yolks and sugar; gradually add to chocolate, stirring constantly. Cook and stir for 2-3 minutes. Remove from heat; cool to room temperature. Fold in whipping cream.
Place half of the bag of mini marshmallows on the bottom of a greased 9 x 13 dish. Add the other half of the bag into the chocolate cream mixture and pour over bottom layer.
Cover and refrigerate overnight. Before serving, top dish with Cool Whip and spoon out servings.