Preheat oven to 325 °F
In a medium saucepan, heat and stir in 1 cup of the cream, the milk chocolate and the semisweet chocolate over low until chocolate melts. Gradually whisk in the remaining cream. Bring to a simmer. Remove from heat.
Bring a tea kettle full of water to a boil.
Whisk egg yolks, sugar, vanilla, and salt in a medium bowl until smooth. Slowly whisk hot chocolate mixture into egg mixture.
Place six 6-oz. ramekins or custard cups in a 3-qt. rectangular baking dish. (9x13) Divide chocolate mixture among ramekins. Place baking dish on oven rack. Pour enough boiling water into dish to reach halfway up sides of ramekins.
Bake 40 to 45 minutes* or until custards are set (centers will shake slightly). Remove ramekins from water. Cool on a wire rack. Cover and chill 4 hours or overnight.
Sprinkle crushed graham crackers over custards. Top each with 3 to 4 Tbsp. of marshmallow creme.
Toast the marshmallow creme using a kitchen torch by moving the tip of the flame across the surface of the creme until golden and slightly puffed. (Watch carefully because marshmallow creme can burn quickly.) Serve immediately.