First mix the icing sugar and vanilla with the egg.
Then add cocoa to the mixture.
Add the melted butter while its still hot.
Then add the crumbled biscuits to the mixture and mix them like a dough.
Pour your mixture on an aluminium foil. (If you want you can also put a plastic film on the foil.)
Fold it like a pyramid and put in the freezer at least 2-3 hours.