Break the chocolate bar into pieces. Place the marshmallows, chocolate and milk in a large microwave-safe bowl. Microwave for 2 minutes and then stir. If needed, microwave an additional 30 seconds and stir until the mixture is fully melted and smooth.

Place the bowl in the refrigerator until COLD.

Crush the Graham crackers in a food processor or by placing in a Ziploc bag and crushing with a rolling pin. Melt the butter and pour into the pie plate. (If using a microwave-safe pie plate, use this for the microwave step). Add the crushed Graham crackers and stir to coat.

Press the mixture evenly onto the bottom and sides of the pie plate. Place in freezer to cool.

Once the chocolate mixture is cold, whip the cream until stiff.

Pour into the Graham cracker crust and freeze at least 6 hours.