S'mores Icebox Cake

Make marshmallow cream: Using a stand or hand mixer, beat 2 cups cream until stiff peaks form, 5 minutes. Add marshmallow fluff and keep beating, 3 minutes. Stir in 1 cup mini marshmallows and set aside. Make ganache: Heat remaining heavy cream until simmering. Remove from heat and pour over chocolate chips in a heat-proof bowl. Let sit 5 minutes, then stir until combined and creamy. In a 9-x-9" baking dish, spread a thin layer of marshmallow cream layer. Top with one layer graham crackers, then top with a thick layer marshmallow cream and then a layer of ganache. Repeat layers until you reach the top (leave about 1/4"). Garnish with remaining mini marshmallows, crushed graham crackers, and chopped chocolate and cover loosely with plastic wrap. Refrigerate at least 4 hours and up to overnight. When ready to serve, heat broiler. Broil 1 minute to toast marshmallows. Freeze 5 minutes to let set and serve.