When I go back home to visit, I ask for one of two cakes. Okay, maybe sometimes I ask for both. There’s the light, fluffy Three Layer Cake, an excellent mid-afternoon pick-me-up. And then there’s dark, rich, and decadent Chocolate Marshmallow Cake– basically if the dessert course had its own dessert.
Chocolate marshmallow cake is the kind of cake where all the adults beg for the smallest square inch while secretly wanting the kid’s size slice. How do I know this? Because we’ve all found each other sneaking more within hours of putting it away.
We normally make this as a sheet cake, with a chocolatey confectioner’s frosting. And while really nothing is ever going to beat the original, Chocolate Marshmallow Cake like all else is up for adaptations. You can take it in any direction, including a round layer cake with a glossy smooth ganache. Ohhhh yeah.
Changing Up the Cake Pans
I talk a lot about perfecting cake texture in the Three Layer Cake post. Same rules apply here.
What’s really interesting is trying to change the size of your pan and still produce spectacular results. This is what went down in my kitchen this week, as I recently got some brand new Fat Daddio’s round cake pans and wanted to give them a spin with this recipe.
Hopefully, it goes without saying that if you use a smaller size pan, the cake layer will be thicker and vice versa. But how do you know what adjustments to make specifically? From ingredients to baking time, where do you begin?
Enter the only type of math I like- cooking math.
If you plan on changing up the pan size, you’ll need to have an idea of the surface area of each, pre and post.
With any four-sided pans, that’s found by multiplying the length of one side by the other. For example, a 9-inch by 13-inch rectangular pan has a surface area of 117 square inches (9 inches x 13 inches = 117 inches squared).
With round pans, you’ll need pi. Not pie. Pi. The 3.14 thing from middle school? You’ll need to take the radius (half the diameter of your pan), square it, and multiply the result times pi. For example, a 9 inch round pan has a radius of 4.5 inches. That squared, times pi equals 63.6 square inches (4.5 in x 4.5 in x 3.14 = 63.585 inches squared).
Comparing the two pans’ surface areas, you’ll notice that the surface area of the 9-inch round is just under half the surface area of the 9×13 cake pan. So, if you double the recipe from round to rectangle, you should end up with a very close approximation of the same cake, thickness and all.
Going bigger usually means cooking longer though, especially so if you plan to increase the depth of your cake. So carefully watch the clock and have toothpicks at the ready. Same with going smaller- cut the original baking time in half and start checking then. No one wants overcooked cake!
Confectioner’s Frosting versus Ganache
As I mentioned earlier, you can top this cake however you like. The original confectioner’s frosting is my favorite. Not quite a buttercream, but still whipped and fluffy, the surface of confectioner’s frosting will harden slightly after coating. This outer shell helps to lock in the cake’s moisture while still being soft and delicious underneath. The flavor is not as dark and moody as ganache, so it lightens up what’s already an intensely chocolatey experience.
But hands down, ganache wins in terms of looks. It’s silky and shiny and stops you in your tracks. Perhaps the simplest of glazes, equal parts semi-sweet or dark chocolate chunks (or chips!) and simmering hot heavy cream will have your cake dressed to the nines in no time. Some recipes will even call for a bit of butter for extra glossiness.
The trick to ganache is allowing the chocolate to sit a few minutes in its hot cream bath. Stirring right away doesn’t allow the chocolate enough time to warm up.
Regardless of which direction you decide to take this cake, it’s eager to prove that marshmallows are not just for campfires and candied yams.
Chocolate Marshmallow Cake
Because marshmallows are not just for campfires and candied yams.
For the batter
- 1 1/2 cups flour
- 4 Tablespoons cocoa powder
- 1/2 teaspoon fine sea salt
- 2 sticks unsalted butter room temperature
- 2 cups sugar
- 4 eggs
- 2 teaspoons vanilla extract
For the topping
- 1 stick unsalted butter room temperature
- 1/2 cup milk
- 1 16 ounce box confectioner's sugar
- 1/2 cup cocoa powder
- 1 10 ounce bag mini marshmallows
For the cake
Preheat the oven to 350 degrees Fahrenheit. Prepare a lightly colored 9-inch by 13-inch cake pan by greasing the bottom of the pan.
Combine all the dry ingredients together in a large bowl and mix.
Cream the room temperature butter and sugar together with a stand mixer, about 3-4 minutes on moderate speed or until light, fluffy and aerated.
Add the eggs one at a time, beating lightly after each to incorporate them into the batter. Add the vanilla and mix briefly once more to combine all wet ingredients.
Slowly combine the dry ingredients with the wet ingredients in the stand mixer bowl, scraping the sides with a spatula as needed.
Pour the batter into the prepared cake pan, and bake for approximately 30 minutes or until batter is set and a toothpick inserted into the middle comes out clean.
For the topping
While the cake is baking, use a hand mixer to combine the butter, milk, and cocoa. Add the confectioner's sugar 1/2 cup at a time until you've reached the desired consistency. Cover with plastic wrap until ready to use.
Immediately after the cake comes out of the oven, cover the top with marshmallows, then coat with the confectioner's frosting.
If using a ganache topping, place 1 cup of semi-sweet or dark chocolate chunks (or chocolate chips) in a medium bowl. Heat 1 cup of heavy cream in a small saucepan or in the microwave with a microwave-safe container until lightly simmering. Immediately pour the hot cream on top of the chocolate, and cover to contain the steam, about 5 minutes. Uncover and stir with a whisk until all the chocolate has melted and forms a smooth, shiny sauce.