White Mountain Layer Cake with Marshmallow Buttercream
Before Ingredient, I didn’t bake. The precision and patience required to complete a bake drives me mad. And then there’s the chance you won’t know something is a disaster until the end. Hard pass. I’ll stick to cooking thankyouverymuch.
My pre-bake routine
- Playlist on
- Recipe read fully. Twice.
- All ingredients prepped exactly as listed, both weight and temperature
My latest adventure in baking was to tackle BraveTart’s (aka. Stella Parks) White Mountain Layer Cake with Marshmallow Buttercream. *gulp* Three layers. Okay. Homemade frosting. I can do this. Oh, you have to make homemade marshmallows for the frosting first?! *gulp*
The reviews made it worth it...
“It tastes like wedding cake.”
“It’s so light.”
“The frosting is delicious. I was expecting it to be sweeter, but I like that it isn’t.”
“It reminds me of angel’s food cake.”
White Mountain Layer Cake with Marshmallow Buttercream
- 1 packet (2 1⁄4 teaspoons) unflavored gelatin powder
- 1⁄4 cup (2 ounces) cool tap water to bloom the gelatin
- 1 tbsp. vanilla extract and/or 1 vanilla bean
- 3⁄4 cup (6 ounces) water for the sugar syrup
- 3⁄4 cup plus 2 tablespoons (10 ounces) light corn syrup
- 2 cups (14 1⁄2 ounces) sugar
- 1⁄2 teaspoon Diamond Crystal kosher salt (half as much if iodized)
- 5 sticks (20 ounces) unsalted butter, soft but cool–about 65°F
- 4 cups (16 ounces) bleached cake flour such as Swans Down
- 2 sticks (8 ounces) unsalted butter, pliable but cool—about 65°F
- 2⁄3 cup (4 ounces) virgin coconut oil, solid but cream–about 70°F
- 2 1⁄4 cups (16 ounces) sugar
- 2 1⁄2 teaspoons baking powder
- 1 teaspoon baking soda
- 3⁄4 teaspoon Diamond Crystal kosher salt (half as much if iodized)
- 1 cup (8 1⁄2 ounces) egg whites (from 8 large eggs), brought to about 70°F
- 2 tablespoons (1 ounce) vanilla extract
- 1 teaspoon almond extract
- 2 cups (16 ounces) cultured low-fat buttermilk, brought to about 70°F
- To better synchronize the downtime in both recipes, start the Marshmallow Buttercream before the cake. First, make the marshmallow base: In a small bowl, mix the gelatin with 2 ounces (1⁄4 cup) cool tap water and vanilla extract, if using. If using a vanilla bean, split lengthwise with a paring knife, run the flat of the blade down each half to scrape out the seeds, and add to the gelatin without stirring. (Reserve the pod for another project.)
- Combine remaining 6 ounces (3⁄4 cup) water, corn syrup, sugar, and salt in a 3-quart stainless steel pot and set over medium heat. Stir mixture with a fork until bubbling, about 5 minutes, then increase heat to medium-high. Clip on a digital thermometer and cook, without stirring, until the clear syrup registers 250°F, about 8 minutes.
- Transfer thermometer to the bowl of a stand mixer and pour in the hot syrup all at once, scraping the pot with a heat-resistant spatula. Cool to exactly 212°F, about 8 minutes, then add gelatin. With the whisk attachment, mix on low speed until the gelatin is melted, then increase to medium-high and whip until thick, snowy white, roughly tripled in volume, and beginning to ball up around the whisk, about 10 minutes. Scrape into a greased 4-cup container, cover tightly, and let stand at cool room temperature until thick and firm, at least 2 hours, or up to 1 week.
- While the marshmallow cream is resting, start the cake: Adjust an oven rack to lower-middle position and preheat to 325°F. Line three 8-by-3-inch anodized aluminum cake pans with parchment and grease with pan spray; if you don’t have three pans, the remaining batter can be held at room temperature for up to 3 hours. (The cakes will brown more and rise less in 2-inch pans.) Sift the flour (if using cup measures, spoon into the cups and level with a knife before sifting) and set aside. Combine butter, coconut oil, sugar, baking powder, baking soda, and salt in the bowl of a stand mixer fitted with a paddle attachment. Mix on low speed to moisten, then increase to medium and cream until fluffy and light, about 5 minutes, pausing to scrape the bowl and beater halfway through. With the mixer running, add the egg whites one at a time, followed by vanilla and almond extracts.Reduce speed to low and sprinkle in one-third of the flour, followed by one-third of the buttermilk. Alternate between the two, allowing each addition to be roughly incorporated before adding the next. Once smooth, fold with a flexible spatula to ensure it’s well mixed from the bottom up. Divide among the prepared cake pans, about 22 ounces each.
- Bake until the cakes are firm but pale, browned only around the very edges, about 40 minutes (or 210°F). A toothpick inserted into the center will emerge with a few crumbs still attached, and your fingertip will leave a slight indentation in the puffy crust. Cool until no trace of warmth remains, about 90 minutes.
- While the cakes are cooling, finish the buttercream. Transfer marshmallow base to the bowl of a stand mixer fitted with the whisk attachment. Whipping on medium speed, begin adding the butter 1 tablespoon at a time, waiting for about 5 seconds after each addition. The fluffy creme will cling to the whisk at first but loosen as the butter is incorporated. Once combined, scrape the bowl with a flexible spatula and whip a minute more. The buttercream should be light and creamy but thick enough to hang upside down from a spoon. If it seems stiff or dense (feeling greasy rather than melting on your tongue), scoop a cup into a small bowl and microwave until completely melted, about 30 seconds. Return the melted buttercream to the bowl and whip 15 seconds on medium-high. Conversely, if it seems loose or gooey, refrigerate the entire bowl 15 minutes, then whip 3 minutes on medium-high.
- Loosen the cakes from their pans with a knife. Invert onto a wire rack, peel off the parchment, and reinvert. Crumb-coat and frost with Marshmallow Buttercream. Serve immediately or store under a cake dome or an inverted pot; the frosted cake will keep for up to 24 hours at room temperature. After cutting, wrap leftover slices individually and store at room temperature for up to 2 days more.