Combine ingredients in large bowl. Working in two batches, pulse ingredients in food processor until chocolate is finely ground. To make hot cocoa, stir 1/3 cup mix into 1 cup hot milk. Top with whipped cream or mini marshmallows.
This hot cocoa mix can be stored in an airtight container for three months. It uses two unusual ingredients: White chocolate chips give the cocoa a soft, creamy texture and escalate the chocolate flavor; and the cornstarch in the confectioners' sugar (an ingredient manufacturers add to prevent clumping) helps thicken the cocoa.