Break the chocolate into small pieces and place in a bowl with the cream. Place over a saucepan of simmering water, without the water touching the bottom of the bowl. When chocolate is melted, let cool slightly.
Beat the butter with the icing sugar until smooth. Slowly beat in the chocolate. Add rum essence and mix well. Place in the fridge and chill a few hours.
Using a spoon, shape a chocolate ball around each almond. Roll in cocoa powder and return to the fridge until serving.