Ingredients
Yellow Sponge Cake
- 1 box (15.25 oz) yellow cake mix
- 1 cup whole milk
- 1/2 cup vegetable oil
- 3 large eggs
- 1 large egg yolk (only use the yolk, discard the egg whites)
- 1 teaspoon pure vanilla extract
Marshmallow Cream Filling
- 1¼ cups unsalted butter (softened)
- 1 jar (7 oz) marshmallow fluff
- 4 cups powdered sugar (sifted)
- 3-4 tablespoons heavy whipping cream
- 1¼ teaspoons pure vanilla extract
- ¼ teaspoon sea salt
Instructions
- Preheat and Prepare Pans: Preheat the oven to 350°F. Line two 9×13 inch cake pans with parchment paper, leaving a slight overhang for easy removal. Lightly spray the parchment paper with nonstick cooking spray. Alternatively, you can skip parchment and spray the pans thoroughly with nonstick spray.
- Make Yellow Sponge Cake Batter: In a large mixing bowl, combine the yellow cake mix, whole milk, vegetable oil, 3 whole large eggs, 1 large egg yolk, and 1 teaspoon vanilla extract. Beat on medium speed for 2 to 3 minutes until the batter is smooth and slightly thick.
- Divide and Bake Cake: Evenly divide the batter between the two prepared pans, spreading each layer thinly and evenly. Bake on the center oven rack for 15-20 minutes or until the tops are lightly golden and a toothpick inserted comes out clean or with a few moist crumbs.
- Cool Cakes: Remove the cakes from the oven and let them cool completely in the pans for about 1 hour.
- Prepare Marshmallow Cream Filling: In a large bowl, beat the softened butter on medium speed for 1-2 minutes until creamy and pale. Add the marshmallow fluff and continue beating until fully combined and fluffy, about 1 minute.
- Add Powdered Sugar: Gradually add the sifted powdered sugar, beating first on low speed and then increasing speed to smooth the mixture, scraping down the bowl sides as needed.
- Finish Filling: Add 3 tablespoons heavy whipping cream, 1¼ teaspoons vanilla extract, and ¼ teaspoon sea salt. Beat on medium speed until the filling is light, fluffy, and holds shape. Add the remaining tablespoon of heavy cream if needed to reach desired spreadability.
- Assemble Cake: Lift one cooled cake layer from the pan using parchment paper overhang or invert the pan to release it, then place it on a serving platter or keep it in the pan if preferred.
- Spread Filling: Spread the marshmallow filling evenly over the first cake layer in a thick, generous layer, leaving a small border around the edges.
- Add Second Cake Layer: Carefully place the second cake layer on top of the filling and gently press down to secure.
- Serve or Refrigerate: Serve the cake immediately or cover with plastic wrap and refrigerate for 6-8 hours or overnight to allow flavors to meld and the filling to set.
- Optional Whipped Cream Topping: For an extra indulgent touch, whip 1.5 cups heavy whipping cream with 1/3 cup powdered sugar until stiff peaks form and serve on top of each slice.
Notes
- Use room temperature butter, softened for easier mixing in the filling.
- Skipping parchment paper is possible if you spray the pans thoroughly with nonstick spray.
- The cake batter will be thin; this is expected for a light sponge texture.
- Refrigerating the assembled cake helps the filling firm up and flavors blend better.
- If the marshmallow filling is too thick to spread, add the remaining tablespoon of heavy cream gradually.
- Leftover heavy whipping cream can be used for homemade whipped cream to serve with the cake.
- Prep Time: 20 minutes
- Cook Time: 20 minutes
- Category: Dessert
- Method: Baking
- Cuisine: American
