Combine chocolate, cream, and butter in top of double boiler. The trick to using a double boiler is to get the water steaming hot - but not boiling hot. You don't want to risk burning the chocolate. Whisk frequently until the chocolate has melted.

Add sugar and yolks and whisk until smooth. Remove from heat and stir in the vanilla.

Place in flat dish and chill until malleable - about 2 hours.

To roll out the truffles, first, pour the graham crackers into a small bowl. Then scoop out about a tablespoon of the chocolate, wrap it around a marshmallow, and roll it into a ball, finish by rolling it in the graham cracker. Continue until you have used all of the chocolate.

Keep refrigerated.