To the bowl of a large capacity food processor (9 cup size or larger), add the cocoa powder, dried milk powder, salt and chopped chocolate, and process until chocolate is very finely chopped and no large pieces of chocolate remain. Add the powdered sugar and process for 20 seconds more, until fully combined. Store the homemade hot chocolate mix in a jar with a tight fitting lid or airtight container for up to 3 months.
Hand Mixing Method
Finely grate the chocolate, using a rasp or the small holes of a box grater. Set aside.
In a large mixing bowl, sift together the cocoa powder, powdered sugar and salt. Stir in the dried milk powder and the grated chocolate. Store the homemade hot chocolate mix in a jar with a tight fitting lid or airtight container for up to 3 months.
To prepare hot chocolate:
Warm milk in a saucepan and whisk in hot chocolate mix to taste. I recommend using 1/3 cup of mix per serving, or more to taste. Add a dash of vanilla to the hot chocolate. Ladle into mugs and top with whipped cream, chocolate shavings or marshmallows.