Grease and line base and sides of a 6cm-deep, 19cm (base) square cake pan with baking paper, allowing paper to extend 2cm above edges of pan. Combine cookies, peanuts, sultanas and cocoa in a bowl.
Place butter, chocolate and condensed milk in a medium saucepan over low heat. Cook, stirring, for 3 to 4 minutes or until smooth. Pour over cookie mixture. Stir well to combine. Spoon mixture into prepared pan, pressing with the back of the spoon. Cover and refrigerate for 2 hours or until set.
I would omit this ganache. Make chocolate ganache: Place chocolate and butter in a small saucepan over low heat. Cook, stirring, for 1 to 2 minutes or until smooth. Remove from heat. Stand for 5 minutes. Spread ganache over slice. Refrigerate for 2 hours or until set. Lift slice from pan. Dust with cocoa powder. Cut into squares. Serve.
