1. Chop the chocolate very fine with a paring knife and place the pieces in a small saucepan with the milk. Place the pan over medium-high heat and stir constantly with a wooden spoon until the chocolate melts and the mixture comes to a boil. Remove from the heat.
2. Place the flour in a small bowl, whisk 1/2 cup of the chocolate into the flour in a slow stream, and continue to whisk until the mixture is completely smooth. Whisk this mixture back into the hot chocolate and bring to a boil again, whisking constantly.