Strawberry Marshmallow Sheet Cake

Ingredients

• 2 ¾ cups unbleached cake flour
• 2 tsp. baking powder
• ¾ tsp. kosher salt
• ½ tsp. baking soda
• 1 lb. very ripe fresh strawberries, hulled, divided
• 1 ½ cups granulated sugar
• ¾ cup unsalted butter, softened
• 1 large egg, at room temperature
• 2 large egg whites, at room temperature
• ⅓ cup whole buttermilk
• 1 ¾ tsp. vanilla extract
• 2 Tbsp. freeze-dried strawberries (from 1 [0.8-oz.] pkg.)
• ¾ cup butter
• 1 (7-oz.) container marshmallow creme
• 2 cups powdered sugar
• 1-2 Tbsp. whole milk

Instructions

1. 1Preheat the oven to 350°F. Grease a 13-by-9-inch baking pan with baking spray and line the bottom with parchment paper. In a medium bowl, whisk the cake flour, baking powder, kosher salt, and baking soda until well combined.
2. 2Put one cup of the fresh strawberries into a food processor and pulse three to five times until roughly chopped, then set them aside. Process the remaining strawberries for about 30 seconds until they form a smooth puree, yielding roughly three-quarters of a cup. Set the puree aside.
3. 3In a stand mixer fitted with a paddle attachment, beat the granulated sugar and softened butter on medium-high speed for about three minutes until pale and fluffy. Add the whole egg, followed by the egg whites one at a time, mixing on medium speed just until blended. Mix in the buttermilk, vanilla extract, chopped strawberries, and strawberry puree for about 30 seconds until combined. Turn the mixer to low speed and gradually add the dry flour mixture in three parts, mixing just until incorporated and scraping down the sides of the bowl as necessary.
4. 4Pour the batter into the prepared baking pan and spread it into an even layer. Bake for 30 to 35 minutes, or until the edges turn golden and a wooden pick inserted into the center comes out clean. Move the pan to a wire rack and let the cake cool completely for about an hour and a half.
5. 5Grind the freeze-dried strawberries in a clean food processor for one minute until they become a fine powder, then set aside. In a stand mixer, beat the butter on medium-high speed for two minutes until creamy. Add the marshmallow creme and beat for another two minutes. Turn the speed to low, mix in one cup of powdered sugar, then add one tablespoon of milk, the strawberry powder, and the remaining cup of powdered sugar. Beat until completely smooth, adding a second tablespoon of milk if the frosting feels too stiff, and chill until needed.
6. 6Spread the chilled berry-marshmallow frosting evenly over the top of the cooled cake. Slice into squares and serve immediately.

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