Line a sheet pan with aluminum foil or baking paper. Place chopped chocolate in a heatproof bowl.
In a saucepan, combine cream and butter. Place over low heat, and bring to a boil. Pour over chocolate, and stir until chocolate is melted and smooth. Stir in cake crumbs and rum. Set aside until firm, but not hard.
Roll heaped teaspoons of this chocolate mixture into balls, then roll in the chocolate sprinkles. Place on the prepared tray. Refrigerate 30 minutes or until firm.