Classic Marshmallow Layer Cake

Ingredients

• 0.5 cup Unsalted butter, softened (113g)
• 1.5 cups Granulated sugar (300g, for the cake)
• 0.5 cup Whole milk (120ml)
• 2 cups All-purpose flour (240g)
• 3 teaspoons Baking powder (1 tablespoon)
• 0.25 teaspoon Cream of tartar (For the cake batter)
• 5 units Large egg whites (Separated, for the cake)
• 1 teaspoon Vanilla extract (For the cake)
• 0.25 teaspoon Salt (For the cake batter)
• 1.5 cups Granulated sugar (300g, for the marshmallow cream)
• 0.5 cup Water (120ml, for the marshmallow cream)
• 2 tablespoons Light corn syrup (Helps prevent crystallization in frosting)
• 3 units Large egg whites (Separated, for the marshmallow cream)
• 1 teaspoon Vanilla extract (For the marshmallow cream)
• 0.125 teaspoon Salt (Pinch, for the marshmallow cream)

Instructions

1. 1Preheat your oven to 350°F (175°C). Grease and flour two 8-inch or 9-inch round cake pans. Line the bottoms with parchment paper for easy removal, then grease and flour the parchment as well. This ensures the cake doesn't stick.
2. 2In a medium bowl, whisk together the all-purpose flour, baking powder, cream of tartar, and salt. Set aside.
3. 3In a large mixing bowl, using an electric mixer on medium speed, cream together the softened unsalted butter and 1½ cups of granulated sugar until light and fluffy, about 3-5 minutes. Scrape down the sides of the bowl as needed.
4. 4Beat in 1 teaspoon of vanilla extract into the creamed butter and sugar mixture until just combined.
5. 5With the mixer on low speed, gradually add the dry ingredients to the wet ingredients in three additions, alternating with the milk in two additions, beginning and ending with the dry ingredients. Mix until just combined after each addition, being careful not to overmix.
6. 6In a separate clean, dry bowl, using an electric mixer with a whisk attachment, beat the 5 large egg whites on high speed until stiff peaks form, about 3-4 minutes. Be careful not to overbeat.
7. 7Gently fold the whipped egg whites into the cake batter in two additions using a spatula. Be careful not to deflate the egg whites, as they provide lightness to the cake.
8. 8Divide the batter evenly between the two prepared cake pans. Bake for 25-30 minutes, or until a wooden skewer inserted into the center comes out clean. The cakes should be lightly golden and spring back when gently touched.
9. 9Let the cake layers cool in the pans on a wire rack for 10-15 minutes before inverting them onto the wire rack to cool completely. This can take up to an hour. Ensure cakes are completely cool before frosting.
10. 10In a small saucepan, combine 1½ cups of granulated sugar, ½ cup of water, and the light corn syrup. Cook over medium-high heat, stirring occasionally, until the sugar dissolves and the mixture comes to a boil. Continue to boil without stirring until the syrup reaches 240°F (115°C) on a candy thermometer (soft-ball stage). This usually takes about 5-8 minutes.
11. 11While the syrup is cooking, in a large, very clean mixing bowl, beat the 3 large egg whites and a pinch of salt with an electric mixer on high speed until soft peaks form, about 3-4 minutes.
12. 12Once the syrup reaches 240°F (115°C), slowly and carefully pour the hot syrup in a thin, steady stream into the whipping egg whites, with the mixer running on high speed. Be careful not to pour the syrup directly onto the whisk. Continue beating on high speed for about 7-10 minutes, until the mixture is very thick, glossy, and holds stiff peaks, and the bowl is cool to the touch.
13. 13Beat in 1 teaspoon of vanilla extract into the marshmallow cream until just combined.
14. 14Place one cooled cake layer on a serving plate. Spread a generous amount of marshmallow cream evenly over the top. Carefully place the second cake layer on top. Spread the remaining marshmallow cream over the top and sides of the entire cake. Serve immediately or store at room temperature for up to 2 days.