Prepare Biscuits

Break the biscuits into small chunks with your hands. Keep some larger pieces for crunch. Place in a large bowl.

Make Chocolate Mixture

In a small saucepan, melt margarine and dark chocolate over low heat. Stir in brown sugar and cocoa powder until dissolved. Add salt, espresso powder, and vanilla extract if using. Stir until smooth and glossy.

Combine

Pour the chocolate mixture over the biscuit pieces. Mix until all pieces are well coated.

Shape the Cake

Line a loaf pan with parchment paper. Transfer the mixture into the pan and press down firmly with the back of a spoon. Cover with plastic wrap and refrigerate (or freeze) for at least 1 hour.

Prepare Topping

In a clean saucepan, heat half the cream with the dark chocolate on low until melted. Remove from heat and stir in the remaining cream.

Top the Cake

Unwrap the chilled cake and pour the chocolate topping evenly over the surface. Smooth with a spatula.

Chill & Serve

Cover again and refrigerate for 3–4 hours, or until topping sets. Sprinkle with crushed biscuits before serving. Slice with a sharp knife for clean edges.