Steps
1. Break the dark chocolate into small pieces and gently melt it with the milk over low heat, stirring continuously until smooth.
2. In a separate bowl, whisk the egg with sugar, salt, and vanilla extract until well combined.
3. Slowly pour the warm chocolate milk mixture into the egg mixture, whisking constantly to prevent curdling.
4. Pour the combined mixture back into a small saucepan.
5. Cook over low heat, stirring constantly until the mixture thickens enough to coat the back of a spoon (about 5-7 minutes).
6. Remove from heat and let it cool slightly before serving.
7. Optional: Chill for 30 minutes in the refrigerator for a firmer texture.