Dump all ingredients into a food processor and pulse until white chocolate chips are finely ground. This makes a large batch, so if your food processor isn't large enough, you may want to do this in two batches. Spoon mixture into an airtight container.
To make a cup of hot cocoa, measure ⅓ cup of hot cocoa mix into a large mug and pour 1 cup of hot milk on top. Stir until everything is completely combined and top with marshmallows or whipped cream if you desire.
Storage instructions: Homemade Hot Cocoa Mix will keep for up to 6+ months stored in an airtight container. As long as the ingredients used are within their expiration date, the mix is still good to use. (Stored properly, of course.)