1 3/4 cups (12 1/4 ounces) sugar
10 tablespoons (1 1/4 sticks) unsalted butter melted and cooled slightly
1. Adjust rack to middle position and heat oven to 350 degrees. Grease two 9-inch-wide by 2-inch high round cake pans; line bottoms with parchment paper. Grease paper rounds, dust pans with flour, and knock out excess. Whisk flour, baking powder, baking soda, salt, and 1 1/4 cups sugar together in large bowl. In 2-cup liquid measuring cup or medium bowl, whisk together butter, buttermilk, vanilla extract, and 6 yolks.
2. In clean bowl of standing mixer fitted with whisk attachment, beat egg whites at medium-high speed until foamy, about 30 seconds. With machine running, gradually add remaining 1/2 cup sugar; continue to beat until soft peaks form, 60 to 90 seconds. Transfer to bowl and set aside.
3. Add flour mixture to now empty mixing bowl fitted with whisk attachment. With mixer running at low speed, gradually pour in butter mixture and mix until incorporated, about 60 seconds. Stop mixer and scrape whisk and sides of bowl. Return mixer to medium-low speed and beat until smooth, 10 to 15 seconds.
4. Stir one-third of whites into batter to lighten; add remaining whites and gently fold into batter until no white streaks remain. Divide batter evenly between prepared cake pans, spread batter to pan walls and smooth tops.
5. Bake until cake begins to pull away from sides of pans and toothpick inserted in center comes out clean, 20 to 25 minutes. Cool cake in pan on wire rack for 10 minutes. Loosen cakes from sides of pan with small knife, then invert onto greased wire rack; peel off parchment. Invert cakes again; cool completely on rack, about 1 1/2 hours.
Chocolate buttercream frosting
8 tablespoons unsalted butter (1 stick)
1/3 cup sugar
2 tablespoons corn syrup
2 teaspoons vanilla extract
1/4 teaspoon table salt
1 1/4 cups heavy cream (cold)
1) Melt chocolate in heatproof bowl set over saucepan containing 1 inch of barely simmering water, stirring occasionally until smooth. Remove from heat and set aside. Meanwhile, heat butter in small saucepan over medium-low heat until melted. Increase heat to medium; add sugar, corn syrup, vanilla, and salt and stir with heatproof rubber spatula until sugar is dissolved, 4 to 5 minutes. Add melted chocolate, butter mixture, and cream to clean bowl of standing mixer and stir to thoroughly combine.
2) Place mixer bowl over ice bath and stir mixture constantly with rubber spatula until frosting is thick and just beginning to harden against sides of bowl, 1 to 2 minutes (frosting should be 70 degrees). Place bowl on standing mixer fitted with paddle attachment and beat on medium-high speed until frosting is light and fluffy, 1 to 2 minutes. Stir with rubber spatula until completely smooth.
The two best cakes in the class