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Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.

In a large bowl, whisk together the flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt for the chocolate cake.

Add the eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat with an electric mixer on medium speed for 2 minutes.

Carefully stir in the boiling water until the batter is smooth and thin. The batter will be very liquidy.

Pour the batter into the prepared 9x13 inch baking pan. Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.

Let the cake cool completely in the pan on a wire rack. This is crucial before adding the filling.

While the cake cools, prepare the marshmallow cream filling. In a large bowl, cream together the softened unsalted butter and powdered sugar until light and fluffy.

Add the marshmallow fluff, heavy cream, and vanilla extract to the butter mixture. Beat on medium-high speed until well combined and fluffy, about 3-5 minutes.

Once the cake is completely cool, spread the marshmallow cream filling evenly over the top of the cake.

Chill the cake with the filling for at least 30 minutes to allow the filling to set slightly.

Prepare the chocolate ganache glaze. In a small saucepan, heat the heavy cream over medium heat until it just begins to simmer. Remove from heat.

Add the semi-sweet chocolate chips and light corn syrup to the hot cream. Let sit for 5 minutes, then whisk until smooth and glossy.

Pour the warm ganache over the chilled cake, spreading it evenly with an offset spatula or the back of a spoon. If desired, use a textured metal scraper to create subtle ridges.

Chill the cake again for at least 30 minutes to allow the ganache to set.

Prepare the white swirl decoration. In a small bowl, whisk together the powdered sugar, milk, and vanilla extract until smooth. The consistency should be thick enough to pipe but still flow.

Transfer the white icing to a piping bag fitted with a small round tip (or a Ziploc bag with a tiny corner snipped off). Pipe continuous wavy lines across the entire chocolate-glazed cake.

Allow the white icing to set for a few minutes before cutting. Using a sharp knife, cut the cake into individual rectangular snack cakes. For clean cuts, wipe the knife clean between each slice.

Serve immediately or store in an airtight container at room temperature for up to 3 days, or refrigerated for up to 5 days.


Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.

In a large bowl, whisk together the flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt for the chocolate cake.

Add the eggs, milk, vegetable oil, and vanilla extract to the dry ingredients. Beat with an electric mixer on medium speed for 2 minutes.

Carefully stir in the boiling water until the batter is smooth and thin. The batter will be very liquidy.

Pour the batter into the prepared 9x13 inch baking pan. Bake for 30-35 minutes, or until a wooden skewer inserted into the center comes out clean.

Let the cake cool completely in the pan on a wire rack. This is crucial before adding the filling.

While the cake cools, prepare the marshmallow cream filling. In a large bowl, cream together the softened unsalted butter and powdered sugar until light and fluffy.

Add the marshmallow fluff, heavy cream, and vanilla extract to the butter mixture. Beat on medium-high speed until well combined and fluffy, about 3-5 minutes.

Once the cake is completely cool, spread the marshmallow cream filling evenly over the top of the cake.

Chill the cake with the filling for at least 30 minutes to allow the filling to set slightly.

Prepare the chocolate ganache glaze. In a small saucepan, heat the heavy cream over medium heat until it just begins to simmer. Remove from heat.

Add the semi-sweet chocolate chips and light corn syrup to the hot cream. Let sit for 5 minutes, then whisk until smooth and glossy.

Pour the warm ganache over the chilled cake, spreading it evenly with an offset spatula or the back of a spoon. If desired, use a textured metal scraper to create subtle ridges.

Chill the cake again for at least 30 minutes to allow the ganache to set.

Prepare the white swirl decoration. In a small bowl, whisk together the powdered sugar, milk, and vanilla extract until smooth. The consistency should be thick enough to pipe but still flow.

Transfer the white icing to a piping bag fitted with a small round tip (or a Ziploc bag with a tiny corner snipped off). Pipe continuous wavy lines across the entire chocolate-glazed cake.

Allow the white icing to set for a few minutes before cutting. Using a sharp knife, cut the cake into individual rectangular snack cakes. For clean cuts, wipe the knife clean between each slice.

Serve immediately or store in an airtight container at room temperature for up to 3 days, or refrigerated for up to 5 days.
