1. In a medium bowl, mix grated chocolate and dry milk powder.
2. In a medium saucepan, heat whole milk over medium heat. Once heated, stir in the chocolate mixture and whisk until the chocolate has melted and the mixture is smooth and hot.
3. Pour 1 Tbsp. Armagnac into each mug (four mugs total), then fill each mug with the smooth, hot chocolate mixture. Serve hot, garnished with whipped cream or marshmallows.