National S’mores Day is August 10, and this recipe is perfect for sharing with friends, even without building a fire. As an added perk, you get to wield a torch in the kitchen, which is always a fun technique.
Position the rack in the center of the oven. Preheat the oven to 350 degrees.
Coat the insides of two 9-inch springform pans with nonstick spray, line bottoms with parchment rounds, then spray parchment.
Stir together the graham cracker crumbs, sugar, and melted butter until combined. Pat equal amounts in the bottom of each prepared pan in an even layer. Bake for 6 to 8 minutes or just until starting to dry out to the touch.
Whisk together the flour, sugar, cocoa, baking soda, and salt in a large bowl. Whisk together the water, oil, vinegar, and vanilla in medium bowl. Pour the wet ingredients over the dry and whisk vigorously until combined and smooth. Divide the batter evenly over the crust in the pans. Firmly tap the bottom of the pans on a work surface to dislodge any bubbles.
Bake for about 30 minutes or until a toothpick inserted in the center shows a few moist crumbs. Cool the pans on racks for 10 minutes. Unmold, invert, peel off parchment, and place the cakes directly on racks to cool completely. Layers are ready to fill and frost, or double wrap them in plastic wrap and store at room temperature to assemble within 24 hours.
Combine the finely chopped milk chocolate and cream in a microwaveable bowl and heat in microwave until chocolate is melted; stir gently until smooth (alternately, use top of double boiler). Cool to room temperature, then chill thoroughly, at least 6 hours or overnight. Ganache should be very thick, like the texture if peanut butter.
Place 1 tablespoon of the water in a small cup and sprinkle the gelatin over the top. Allow to soften for 5 minutes. Whisk together the sugar, corn syrup, and 1/3 cup water in a medium-sized saucepan with a candy thermometer clipped to the side. Bring the mixture to a boil over medium heat, stirring until the sugar dissolves.
Meanwhile, beat the egg whites in large bowl with electric mixer until stiff peaks form. When sugar syrup reaches 248 degrees, slowly pour the hot syrup into the egg whites, taking care not to hit sides of bowl or the beaters. Aim for the egg whites themselves. Continue to beat until whites are stiff and glossy, about 5 minutes, and then beat in the vanilla. Microwave the gelatin in 5 second bursts until melted and pour over egg whites with mixer running. Beat marshmallow until cool, about 6 to 8 minutes more.
Beat the cooled ganache in a large bowl with an electric mixer until lightened in color, smooth, and a bit aerated. If it is too stiff to whip, remove a cup of it (do this by eye), microwave until very soft and use this to “seed” the rest of the batch. The ganache should be very smooth and spreadable.
Place one cake layer, graham cracker crust down, on a display plate. Top with a thin layer of ganache, then a thin layer of marshmallow. Top with second cake layer, again, crust side down. Cover top and sides of cake with ganache. Scrape remaining marshmallow on top and sides as well, make decorative peaks here and there with a spoon or icing spatula.
Use a small butane or propane torch to brown the meringue. Alternately, you can broil in oven; just be careful as the marshmallow can burn easily.