Soak the raisins in the rum for 30 minutes. Crumble the biscuits into pieces. Add the rum and raisins to them, the coarsely chopped walnuts, cocoa, milk, soft butter and melted chocolate. Mix everything until you get a homogeneous mixture.
Finally, add the orange peels. Transfer the mixture into a small form. Smooth out the top and press down lightly. Put the cake with crushed biscuits in a refrigerator for several hours before taking it out.
Optionally, on top you can garnish it with melted chocolate, powdered sugar, etc.