1.Preheat oven to 180°C/350°F. Grease a deep 18cm (7¼-inch) square cake pan; line base and sides with baking paper.
2.Stir butter and chopped chocolate in a small saucepan over low heat until smooth; transfer to a medium bowl, cool
3.Stir sugar, egg and flour into chocolate mixture. Spread into pan; bake about 20 minutes. Cool in pan.
4.Cut cake into large pieces; using a food processor, process cake with rum until mixture just comes together. Shape rounded teaspoons of the mixture into balls. Place on a baking paper-lined tray. Freeze 1 hour or refrigerate 3 hours or overnight, until firm.
5.Stir chocolate melts in a medium heatproof bowl over a medium saucepan of simmering water until smooth (don’t let water touch base of bowl). Pour into a heatproof jug.
6.Dip the end of one stick into the chocolate, then push it about halfway into a ball of cake. Return to tray. Repeat with remaining sticks and balls of cake. Freeze for about 5 minutes to set.
7.Dip one cake pop into the chocolate, rocking back and forth to coat; don’t swirl the pop, or it’ll break. Allow excess chocolate to drip back into the jug.
8.Stand on a baking paper-lined oven tray; sprinkle with pearls before chocolate sets. Repeat with remaining cake pops and pearls. Stand at room temperature until set. Serve in paper cases.
Store cake pops in an airtight container at a cool room temperature until ready to serve. They will keep for up to 1 week.Note