1. In a food processor with the knife blade, blend the graham crackers until finely ground, place them in a large bowl.
2. In a medium bowl, combine butter and sweetened condensed milk. Add the cocoa powder and liqueur, mix well.
3. Gradually stir the mixture to the crumbs.
4. Using your hands, form the mixture into the shape of a potato or 1-1.5 inch balls.
5. Decorate with nuts or white cream. Refrigerate for at least 30 minutes.