How to Make It
Prepare the Cake Layers: Preheat oven to 350°F. Grease and flour 3 (8-inch) round cake pans; set aside. Place chopped chocolate in a small heatproof bowl; pour boiling water over chocolate. Whisk until chocolate is melted and smooth. Let stand until cooled to room temperature, about 20 minutes.
Beat butter with a heavy-duty stand mixer fitted with a paddle attachment on medium speed until creamy, about 1 minute. Gradually add granulated sugar and brown sugar, beating until light and fluffy, 3 to 4 minutes. Add egg yolks 1 at a time, beating until just blended after each addition. Add vanilla and cooled melted chocolate, beating until blended. Whisk together flour, cocoa, baking soda, and salt in a separate bowl. Add flour mixture to butter mixture alternately with buttermilk, beginning and ending with flour mixture, beating on low speed until just blended after each addition.
Beat egg whites in a separate bowl with an electric mixer on medium speed until soft peaks form, about 5 minutes. Gently fold into chocolate batter. Pour batter evenly into prepared pans.
Bake in preheated oven until a wooden pick inserted in centers of Cake Layers comes out clean, 20 to 30 minutes. Cool in pans on wire racks 10 minutes. Remove Cake Layers from pans; let cool completely on wire racks, about 40 minutes.
Prepare the Frosting: Beat butter with a heavy-duty stand mixer fitted with a paddle attachment on medium speed until creamy, about 1 minute. Gradually add powdered sugar, vanilla, salt, and 2 tablespoons of the chopped strawberries, beating on medium speed until mixture is creamy with streaks of strawberries throughout. Increase speed to medium-high; beat until light and fluffy, about 1 minute. Gently fold in remaining strawberries.
Place 1 Cake Layer on a platter; spread about 1/2 cup Frosting over top of layer. Repeat process with 1 additional Cake Layer and 1/2 cup Frosting. Top with remaining Cake Layer; spread remaining Frosting over top and sides of cake. Garnish with whole and halved strawberries.