Easy S'mores Sheet Cake

Method

Graham Cracker Cake

Preheat the oven to 350F/177C convection (or 325F/162C conventional) and grease and a 9x13" cake pans with cooking spray and parchment paper.
Place the graham crackers in a food processor and turn it on high until there are no more large chunks. In a medium bowl, whisk together the flour, graham cracker crumbs, baking powder, salt, and cinnamon. Set the dry ingredients aside.
65 grams graham cracker crumbs about 1/2 sleeve or 4-5 sheets of graham crackers , 240 grams all-purpose flour spooned and leveled, 1 tbsp baking powder, 1/2 tsp fine sea salt, 1/4 tsp cinnamon *optional
In an electric mixer fitted with the whisk attachment, beat the butter, oil, granulated sugar, light brown sugar and vanilla extract together, on medium speed, until they’re light and fluffy. This should take 2 to 3 minutes.
56 grams unsalted butter room temperature, 120 mL canola oil or any neutral oil, 100 grams granulated sugar, 200 grams light brown sugar lightly packed, 1 Tbsp vanilla extract
Add the eggs, one at time, beating well after each addition. Make sure to scrape the bottom of the bowl as needed.
3 large eggs room temperature
In five increments, alternate adding the dry ingredients and buttermilk into the batter, beginning and ending with the dry ingredients. Beat the mixture on medium speed, just until the flour is fully incorporated, making sure to scrape the edge of the bowl as needed.
240 mL buttermilk*
Spread the batter evenly in the prepared pan and bake for about 30-35 minutes, until the cake springs back when it’s poked. Remove the cake from the oven and allow it to cool completely before frosting.

Milk Chocolate Ganache

Place the milk chocolate in a medium bowl and in a small saucepan, heat the heavy cream until it's simmering. Pour the heavy cream over the chocolate and let it melt for 1-2 minutes. Stir until the chocolate is completely smooth.
340 grams milk chocolate chips**, 170 mL heavy cream
Allow the chocolate ganache to cool for just a few minutes so it's no longer hot.
Meanwhile, use a straw to poke holes into the cake going down only about 1/2-3/4 of the way. Spread the chocolate ganache on top of the cake. Refrigerate it while you make the meringue.

Meringue Frosting/Marshmallow Frosting

Begin by thoroughly cleaning the aluminum bowl and the whisk attachment of the stand mixer (they can’t have any fat residue when making meringue). Once they’re clean and dry, place the egg whites and the granulated sugar in the bowl.
120 grams egg whites room temperature, 200 grams granulated sugar, 1/4 tsp cream tartar
In a small saucepan, bring 1/2 cup (118mL) of water to a simmer. Keep the water simmering on low heat and place the bowl with the egg whites, sugar and cream of tartar on top of the saucepan, creating a double boiler. Whisk the egg whites and sugar over low heat for about 10 minutes, until the sugar granules are completely dissolved. You can feel it between your fingers if the sugar is fully dissolved or you can use a candy thermometer and bring the mixture to about 175°F (80°C).
When the egg whites reach temperature, remove the bowl from the heat and place it on the stand mixer fitted with the whisk attachment. Beat the mixture on medium-high speed, until stiff peaks form, about 10 minutes.
Add the vanilla and salt and continue beating the mixture until it's well combined. Spread the meringue on top of the set chocolate layer and use a kitchen torch to toast the top.
1 Tbsp vanilla bean paste, tiny pinch sea salt

Notes

*You can use a homemade buttermilk by mixing 1 cup of milk with 1 Tbsp of lemon juice or vinegar.

**S'mores generally uses milk chocolate so I made this more nostalgic but if you're like me and you like an elevated, less sweet s'mores treat, use dark chocolate instead of milk. I recommend adding an extra 1-2 Tbsp of heavy cream if using dark chocolate.

***If you're worried about the meringue weeping, make sure to get a thermometer and take the eggs to 175C - I promise it makes all the difference and don't skip the cream of tartar.

Alternatively if you need the meringue to last a long time, you may add in 1/4 tsp gelatin. Dissolve it in 1-2 tsp of cold water, let it set and then microwave it for 5 seconds before adding it into the fully whipped cream. Mix just until it's well combined. Then when you refrigerate it, the meringue will set a bit and last a long time without weeping - can even be frozen like this.