Grease and line a 20 x 30cm slice tin.
Using a rolling pin, crush the biscuits in a double lined plastic bag to achieve a rough crumb.
Combine the biscuit crumbs and marshmallows in a bowl.
In a saucepan combine the butter, caster sugar and cocoa, stirring over a low heat until smooth. Add the lightly beaten eggs and cook for 5 minutes, stirri