I love a s'more. It’s classic, it’s easy and during summer it’s the ultimate dessert. And while the s'more is possibly the easiest dessert there is, it can become a bit of a production to get all the kids (or adults) sticks for marshmallows and get a fire going, so instead I turn to this make-ahead option that has all the flavors we love but can be made in advance so everyone can enjoy s'more time. The base is a graham cracker and rice cereal bar that is topped with a rich chocolate mousse. Marshmallows are added and bruléed for the classic toasted flavor.
Line an 8-inch-square baking pan with parchment paper, letting the paper hang over two sides of the pan to act as handles. Spray the parchment with non-stick spray.
Place 18 marshmallows (about 4 ounces or 2 cups) in a medium bowl and set aside. Place the remaining 8 ounces of marshmallows (about 4 cups) in a large microwave-safe bowl along with the butter. Microwave on high until the marshmallows and butter are completely melted, about 1 minute, stirring halfway through. Stir to combine. Add the graham crackers and rice cereal and quickly stir them into the melted marshmallows. Immediately scrape the mixture into the prepared pan. Spray the bottom of a measuring cup with nonstick spray and use it to press the mixture into an even layer in the pan.
Place 1 cup heavy cream to a medium microwave-safe bowl. Microwave the cream until it is just starting to steam, about 1 minute. Add the chocolate chips and cocoa powder. Shake the bowl lightly to make sure the chips are completely submerged in the heavy cream. Let stand about 5 minutes. Whisk the heavy cream and chocolate together until smooth. If any chocolate isn’t melted you can microwave for 10-second increments until completely melted. It’s important to only microwave 10 seconds at a time so the mixture never gets too hot. Once melted set aside to cool slightly.
Place the remaining 1 cup of heavy cream in the bowl of an electric mixer or a medium bowl and whip with a mixer or whisk until stiff peaks form. Fold the whipped cream into the melted chocolate until you no longer see any streaks of white. Spoon the mousse over the graham cracker base and smooth the top to make an even layer.
Cut the reserved 18 marshmallows that were set aside in half horizontally. Press 6 marshmallow halves in a row along the bottom border of the pan. Continue adding lines of marshmallows so that you have 6 rows of 6 marshmallows each covering the mousse. Cover with plastic wrap (preferably reusable) and refrigerate for 4 hours or overnight.
When ready to serve, cut the bars into 6 long strips following the lines of the marshmallows. Then cut the strips in half so that each bar has 3 marshmallow halves on it. If desired, toast the marshmallows with a kitchen torch and serve. The bars can be refrigerated up to 3 days.
You can also use a 9-inch-square baking dish to make the bars; each layer will just be slightly thinner.
If the chocolate mixture looks slightly grainy after microwaving, don’t worry; it will become smooth as you fold in the whipped cream.
Propane gas torches are highly flammable and should be kept away from heat, open flame and prolonged exposure to sunlight. They should be used only in well-ventilated areas. Follow torch manufacturer's instructions for use.