Melt in a pan:

500 mls heavy (at least 35%) cream
550 grams 70% cocoa chocolate

Stir in off the heat:
170 grams of unsalted butter (cold, cubed)

Line a shallow dish with cling film and pour in the fontant.  Put it in the fridge until it is solid and then cut it into tiny pieces and eat it quickly.  That is not difficult.