In a saucepan, heat the double cream over low heat until it's warm but not simmering. Add the butter and sugar, stirring continuously until they melt and the sugar dissolves completely into the cream.
Break the chocolate into pieces and add them to the saucepan. Keep stirring until the chocolate melts. Remove from heat and set aside.
In a bowl, break the biscuits into small pieces. Also now put the raisins in the bowl on top of the biscuits.
Pour the warm chocolate sauce over the broken biscuits. Add the rum essence and mix thoroughly until all the biscuit pieces are evenly coated in the chocolate sauce.
Let the mixture cool slightly for about 20 minutes, allowing it to thicken a bit.
Lay a sheet of plastic wrap on a clean, flat surface. Spoon the biscuit mixture onto the plastic wrap, shaping it into a log or salami shape.
Roll the plastic wrap tightly around the log, ensuring there are no air pockets. Twist the ends of the plastic wrap to secure the shape.
Place the wrapped log in the refrigerator and chill for at least 4 hours, preferably overnight, to allow it to firm up completely.
Unwrap the log and roll it in desiccated coconut until it's evenly coated.
Slice the chocolate biscuit roll into rounds, arrange the slices on a plate and serve.
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Notes
If you want perfectly clean slices, chill the log in the freezer for about 30 minutes before slicing. This will help it firm up even more.You can use Milk Chocolate or Semi-Sweet Chocolate, if you prefer a milder chocolate flavour. Keep in mind that the sweetness level of the dessert will increase.Avoid storing at room temperature for extended periods, especially in warm weather, as the chocolate may soften or melt.