• 6 large egg whites , at room temperature
• 1 1/4 cups whole milk , at room temperature
• 2 tsp. vanilla extract | Get the recipe!
• 4 cups cake flour , sifted directly into measuring cup (not self-rising)
• 2 cups sugar
• 4 tsp. baking powder
• 1 tsp. salt
• 16 Tbsp. (2 sticks) unsalted butter , at room temperature, cut into 8 pieces

• 3/4 cup and 3 Tbsp. sugar
• 1 ripe apricot , halved and pitted
• 5 large egg whites , at room temperature
• 24 Tbsp. (3 sticks) unsalted butter , at room temperature
• 3 ounces good-quality white chocolate , melted in the microwave or double-boiler according to package instructions; cooled slightly
• 1 to 2 Tbsp. pistachio paste , to taste

• 1/3 cup apricot preserves or apricot jam

Note: This recipe is for a classic, one-tiered layer cake.

To make cake: Preheat oven to 350°. Grease 2 (9" x 2") 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.

To make buttercream: 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.

To assemble 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.