Place the biscuits in a large bowl.
Use your hands or a rolling pin to roughly crush them. You want a mix of fine crumbs and larger pea-sized pieces for texture. Set aside.
2. Make the Chocolate Mixture
In a medium saucepan, melt the butter over low to medium heat.
Once melted, remove the pan from the heat.
Add the dark chocolate pieces and stir continuously until they are completely melted and the mixture is smooth.
Return the pan to very low heat. Add the milk, powdered sugar, and cocoa powder. Stir well until everything is combined into a rich, smooth sauce. Do not let it boil.
Remove from heat and stir in the vanilla extract (and rum/brandy, if using).
3. Combine and Shape
Pour the warm chocolate mixture over the crushed biscuits in the bowl.
If using, stir in the chopped nuts now.
Use a wooden spoon or spatula to mix thoroughly until all the biscuit pieces are completely coated.
Lay a large sheet of parchment paper (or cling film) on your counter.
Spoon the entire mixture onto the center of the parchment paper.
Use the paper to help you roll the mixture into a tight log shape, about 6-8 inches (15-20 cm) long.
Twist the ends of the paper like a candy wrapper to seal and compress the log, ensuring it holds its shape.
4. Chill and Serve
Place the wrapped log in the refrigerator for at least 3 to 4 hours, or ideally overnight, until it is completely firm.
When ready to serve, unwrap the log.
Optional: Dust the log with powdered sugar or cocoa powder. You can use a fork to drag light lines across the surface for a “wood grain” effect.
Use a sharp knife to slice the log into $\frac{1}{2}$-inch (1 cm) thick slices.
Enjoy! This keeps well in an airtight container in the fridge for up to a week.
