Vanilla Cake with Pistachio & Apricot & Blood Orange & Coconut Buttercreams

Ingredients:
6 large egg whites, at room temperature
1 1/4 cups whole milk, at room temperature
2 teaspoons vanilla extract
4 cups cake flour, sifted directly into measuring cup (not self-rising)
2 cups sugar
4 teaspoons baking powder
1 teaspoons salt
16 T (2 sticks) unsalted butter, at room temperature, cut into 8 pieces
3/4 cup and 3 T sugar
1 ripe apricot, halved and pitted
5 large egg whites, at room temperature
24 T (3 sticks) unsalted butter, at room temperature
3 ounces white chocolate, melted in the microwave or double-boiler according to package instructions; cooled slightly
1 to 2 T pistachio paste, to taste
1/3 cup apricot preserves or apricot jam

1 cup sugar
3 large egg yolks, at room temperature
24 T (3 sticks) unsalted butter, at room temperature
1/3 cup shredded unsweetened coconut, toasted
3/4 teaspoon finely grated blood orange zest or orange zest
1 T blood orange juice or orange juice

Preparing the cake:
Preheat oven to 350 degrees F. Grease 2 (9-inch x 2-inch) round cake pans. Line bottoms with parchment paper; grease parchment and dust pans with flour, tapping out excess. In a small bowl, whisk egg whites, 1/4 cup milk, and vanilla until combined.

In a stand mixer with paddle attachment, combine flour, sugar, baking powder, and salt. Mix on low speed for 1 minute. Add butter and remaining 1 cup milk; mix on low speed until dry ingredients are moistened. Then beat on medium speed for 2 minutes. Add 1/3 egg white mixture and beat on low speed until blended. Beat on medium speed for 20 seconds. Scrape bowl down. Repeat 2 times with remaining egg white mixture. Divide batter between prepared pans and spread evenly. Bake 30 to 40 minutes, or until a toothpick inserted in center comes out clean. Let cool in pans 10 minutes. Run a knife around sides of pans and turn cake layers onto racks; flip layers and let cool completely.

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Preparing the pistachio and apricot buttercreams:
In a small saucepan, bring 3/4 cup water and 3 tablespoons sugar to a boil. Boil for 1 minute. Add apricot; reduce heat to low. Simmer until apricot softens, about 2 minutes. Put apricot on a plate and refrigerate until cool enough to handle; remove peel and finely chop (it will be a puree). Set aside.

Bring a large saucepan filled with about 1 1/2-inches water to a boil; reduce heat so water simmers. Combine egg whites and remaining 3/4 cup sugar in a medium stainless steel bowl. Place bowl over pot of simmering water (bowl should be above, not touching, water) and whisk constantly until egg mixture is warm and sugar dissolves, about 5 minutes.

In a stand mixer with whisk attachment, beat egg white mixture on high speed until stiff peaks form, about 5 minutes. Reduce speed to medium-low and beat until cool, about 8 minutes. Add butter, 1 tablespoon at a time, beating until blended after each addition. Beat on medium-high speed until buttercream is smooth and fluffy, about 1 minute. If at any point buttercream appears separated, beat again until smooth. Add white chocolate and beat until smooth and fluffy. Divide buttercream; stir apricot puree into one half until well blended. In the other half, stir in pistachio paste, to taste.

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Preparing the coconut and blood orange buttercreams:
Combine sugar and 1/3 cup water in a small saucepan and bring to a boil over medium-high heat, stirring to dissolve sugar. Then boil without stirring until syrup reaches 240 degrees on a digital thermometer, about 6 minutes.

Meanwhile, in stand mixer with whisk attachment, beat egg yolks on medium speed until slightly thickened, about 2 minutes. With mixer running, gradually pour in hot syrup in a thin stream; avoid pouring syrup on whisk. Increase speed to medium-high and beat until yolk mixture is thick and cool, about 8 minutes. With mixer on medium speed, add the butter 1 tablespoon at a time, beating until blended after each addition. (If at any time buttercream appears curdled, increase speed to high and beat until smooth; then reduce speed to medium and continue beating in butter.) Divide buttercream evenly between two bowls; stir coconut into one bowl, and blood orange zest and juice into other.

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Assembling the cake:
Remove parchment paper from cake layers. Place 1 layer on a cake stand or serving plate. Spread with apricot buttercream and then preserves. Top with second cake layer, top-side up. Frost cake with about 1 cup pistachio buttercream to crumb coat. Refrigerate 15 minutes. Frost with remaining pistachio buttercream. Serve immediately or refrigerate; if refrigerated, let stand at room temperature 1 hour before serving.