Heat oven to 350°F (325°F for dark or nonstick pans).
Spray bottoms and sides of 3 (8-inch) round cake pans with cooking spray.
In large bowl, beat Cake ingredients with electric mixer on medium speed 2 minutes, scraping bowl occasionally.
Pour 1 2/3 cups batter in each pan.
Spread evenly.
Bake 18 to 22 minutes or until toothpick inserted in center comes out clean.
Cool 10 minutes; remove from pans to cooling racks.
Cool completely, about 1 hour.
In medium glass or metal bowl, beat egg whites and sugar with whisk until blended.
Set over pan of simmering water 16 to 20 minutes, beating occasionally with whisk, until sugar has dissolved and egg mixture reaches 160°F.
Remove from heat; pour into bowl of electric stand mixer fitted with whisk attachment.
Beat on high speed 2 to 3 minutes or until glossy peaks form and bowl has cooled to feel slightly warm.
Still on high speed, slowly add 1 1/2 cups softened butter, one piece at a time, scraping side of bowl occasionally, until mixture is smooth, thick and shiny, 12 to 14 minutes.
Beat in vanilla. If mixture separates, beat until smooth.
Fit decorating bag with 1/2-inch round piping tip; fill with 1 1/4 cups vanilla frosting, and set aside.
In small microwavable bowl, microwave 2 oz chopped chocolate uncovered on High 60 seconds, stirring halfway through microwave time.
Continue to microwave in 10-second increments until chocolate can be stirred smooth.
Let stand 10 minutes.
Beat cooled melted chocolate into remaining frosting until smooth.
Place one cake layer on serving plate.
Spread 2/3 cup chocolate frosting on top.
Top with second cake layer; spread 2/3 cup chocolate frosting on top.
Place third cake layer on top.
Frost side and top of cake with remaining chocolate frosting.
Using decorating bag, pipe frosting mounds on top of cake with vanilla frosting (use photo as guide).
Sprinkle 1 tablespoon chocolate shavings over frosting mounds.