In a medium bowl, mix grated chocolate and dry milk powder.
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.
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.