Keep on fire until the chocolate and sugar dissolve (always stir with a whisk), do not bring to a boil. The liquid should not boil!!!
If the chocolate has not completely dissolved (the chocolate is of poor quality), you can grind it with a blender, but not for long, and then the cream will start whipping.
When the chocolate is completely dissolved, add vodka and let the liquor warm up well, but do not boil!!!