In a medium saucepan over medium low heat, combine the milk, sugar, cocoa, cornstarch and sugar, and stir until smooth. Heat mixture until it just begins to steam.

In a medium bowl, whisk together the egg yolks. Slowly add the milk mixture to the egg yolks in a small stream while whisking constantly. When fully combined, pour back into the saucepan.

Place over medium heat and cook until thickened, about 4-5 minutes, while stirring constantly. Remove from heat and add vanilla extract. Chill in the fridge for at least 1 hour.

In the bowl of a stand mixer fitted with a whisk attachment, or with a large bowl and a hand-held mixer, beat the marshmallow cream and heavy cream to soft peaks. Fold in the mini marshmallows.

Line a 9x5-inch loaf pan with plastic wrap. Place a row of graham crackers on the bottom (you may need to break some in order to make them fit). Top with the marshmallow whipped cream. Then spread on a layer of the chocolate pudding.

In the bowl of a stand mixer fitted with a whisk attachment, or with a large bowl and a hand-held mixer, beat the heavy cream, sugar, and vanilla to medium peaks.

Remove the plastic wrap from the top of the icebox cake. Place a serving platter upside-down on top the icebox cake, then invert the whole thing so that the cake is now sitting on the platter. Gently remove the loaf pan and plastic wrap.

Cover the icebox cake in the whipped cream. Top with broken graham crackers and mini marshmallows. If desired, use a kitchen torch to toast the marshmallows, working quickly so you don't melt the whipped cream. Drizzle with chocolate syrup.

Store leftovers in the fridge for up to 5 days.