For cake: Preheat oven to 350°F; grease and flour 3 (9-inch) cake pans.
In a large bowl, beat butter at medium speed with electric mixer until creamy. Gradually add sugar, beating until fluffy.
Add egg whites, one at a time, beating well after each addition. Beat in vanilla.
In a small bowl, combine cake flour, baking powder, and salt; sift twice. Add flour mixture, alternately with buttermilk, beginning and ending with flour mixture. Stir in melted chocolate.
Pour batter evenly into prepared pans; bake for 23 to 25 minutes, or until a wooden pick inserted in center comes out clean. Let cool in pans for 10 minutes. Remove cakes from pans and allow to cool completely on wire racks.
Spread 1/4 cup strawberry preserves between each cake layer.
Spread White Chocolate Frosting on sides and top of cake. Break pirouette cookies in half and place (vertically, edges touching) around sides of cake, if desired. Top with white chocolate curls, if desired.
For White Chocolate Frosting (Makes about 3 cups):.
In a medium bowl, combine chocolate and cream. Microwave on high in 30-second intervals, stirring between each, until chocolate is melted and smooth (about 1 1/2 minutes total); let cool completely.
In a large bowl, combine white chocolate mixture, butter, and vanilla. Beat at medium speed with an electric mixer until smooth. Gradually beat in confectioners' sugar until fluffy.