Place the chocolate in the fridge 30 minutes before making the mix. Break the chocolate into smaller pieces and transfer it in a food processor. Being cold ensures that the chocolate doesn't melt during processing. Pulse until the chocolate is finely ground.
Add the remaining ingredients and pulse 2-3 times until well combined.
If you don't have a food processor, grate the chocolate on a fine grater then sift the cocoa, cornstarch, powdered milk, sugar and salt in a bowl and stir in the grated chocolate.
Store the hot chocolate mix in an airtight container or in a sealed glass jar.
To prepare the hot chocolate:
Bring 1 cup of milk to a boil in a small saucepan.
Stir in 1½ - 2 tablespoons of hot chocolate mix and stir well with a whisk for 1-2 minutes over low heat until it thickens.
Pour into a mug and serve hot.
Optional: add ground cinnamon, cardamom, star anise or ginger into the hot chocolate mix for a spiced version. Serve the prepared hot chocolate topped with mini-marshmallows, chocolate shavings or a dollop of whipped cream.
Recipe by Pastry Workshop at http://pastry-workshop.com/hot-chocolate-mix-mix-pentru-ciocolata-calda/