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Vanilla Hostess Sheet Cake

This homemade Vanilla Hostess Sheet Cake is a nostalgic throwback to your favorite childhood snack—made better! A soft and fluffy vanilla cake is layered with marshmallow vanilla cream filling, then finished with the iconic white swirl on top (no glaze needed!). It starts with a boxed mix but gets major flavor upgrades with sour cream, milk, and vanilla. Easy to make, super fun to serve, and perfect for birthdays, bake sales, or just because.
Prep Time20 minutes
Cook Time30 minutes
Chill Time1 hour
Course: Dessert
Servings: 20 slices
Author: Emily - My Messy Kitchen

Ingredients

For the cake:

  • 1 box yellow cake mix 15.25 oz
  • 1 cup all-purpose flour
  • 1 cup granulated sugar
  • 3 eggs room temperature
  • 1 ¼ cups whole milk room temperature
  • ½ cup sour cream room temperature
  • ¼ cup vegetable oil
  • 1 tsp vanilla extract

For the filling:

  • ¾ cup unsalted butter
  • 7 oz marshmallow cream
  • 2 cups powdered sugar
  • 1 tsp vanilla extract
  • 2-3 tbsp heavy cream
  • pinch of salt

Instructions

For the cake:

  • Preheat oven to 325°F. Grease a 9x13-inch pan, line with parchment paper, and set aside. If using two pans, prepare two pans.
  • In a large bowl, whisk together cake mix, flour, sugar, and salt. In another bowl, whisk together eggs, milk, sour cream, oil, and vanilla until smooth. Pour wet ingredients into dry and mix until just combined. Batter will be thick and creamy.
  • Pour into the prepared pans and bake for 30-35 minutes in 1 pan or 25-28 minutes in two, or until a toothpick inserted in the center comes out clean. Let cool completely in the pans on a wire rack before frosting.

For the filling:

  • Beat the butter until smooth and fluffy. Add marshmallow fluff and mix until combined. Slowly mix in powdered sugar, vanilla, and salt. Add cream or milk only if needed to smooth it out. You want it thick but spreadable—not runny.

For assembly:

  • Once the cake is fully cooled, if you only used 1 pan carefully slice it in half horizontally using a long serrated knife. (Tip: chill the cake for 20–30 minutes first to make slicing easier.)
  • Take out 1/4 cup of the filling and add to a piping bag fitted with a small round tip. Spread the rest of the marshmallow filling evenly over the bottom layer, then gently place the top half or second sheet cake on top.
  • Pipe swirls across the top. Chill in the refrigerator for at least 30 minutes to make slicing easy! Store covered at room temperature for up to 2 days, or in the fridge for up to 5.