Heat oven to 180°C. Grease bottoms only of 2 (20 or 23cm) round cake pans with shortening or cooking spray.
In large bowl, beat yellow cake ingredients with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Set aside.
In another large bowl, beat chocolate cake ingredients on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally.
Spoon yellow and chocolate cake batters alternately into pans, dividing evenly. Cut through batters with table knife in zigzag pattern for marbled design.
Bake 40 to 45 minutes or until toothpick inserted in center comes out clean. Cool in pans on cooling racks 15 minutes. Remove from pans. Cool completely, top sides up, about 1 hour.
On a serving plate, place 1 cake, rounded side down (trim rounded side if necessary so cake rests flat). Spread with 55 grams frosting. Top with second cake, rounded side up. Frost side and top of cake with remaining frosting.