Heat the cream (but do not boil) and melt the chopped chocolate bars in it. Season to taste with a few squirts of lemon juice. If you like the sauce less sweet, add more cream or lemon juice.
It can be enjoyed warm or cold. I prefer the cold version (leave it covered overnight) it is then very frothy and not so sweet. A dream with vanilla ice cream with cherries (e.g. thickened in mulled wine stock).