Put the biscuits in a bag and use a rolling pin to crush them into small pieces. Avoid turning them into powder—texture is important.

In a saucepan, combine cocoa, sugar, butter, and milk. Heat on low, stirring until the butter melts and the mixture becomes smooth. Add rum essence for flavor.

Pour the cocoa mixture over the crushed biscuits. Add walnuts and dried fruits if using. Combine everything thoroughly until all the biscuit fragments are evenly covered.

Transfer the mixture onto plastic wrap. Shape it into a log (like a salami) and wrap it tightly. Twist the ends to seal.

Chill for a minimum of 4 hours or until it becomes firm. Dust with powdered sugar before slicing into 1–2 cm thick rounds.