I've always wanted to try this one. Now I have. Probably will never do it again. Okay, maybe for a dear niece or nephew someday when I get to be there for a birthday. The cake itself wasn't bad at all. Of course I cheated and used a box mix which I'm sure saved me a good hour or so. The frosting was what had me nervous. There are certain things that just do not do well in my presence: yeast, living plants, egg whites and cooking sugar. But my dearest was tired of the plain ole' butter cream, so I risked the inevitable flop. And then the unthinkable happened, it worked! Somehow I pulled of the frosting and I was happy beyond belief. Be warned - the frosting ALONE contains a full pound of butter. That's 4, count them, four sticks of the glorious golden stuff. So be sure that you have a good number of people to feed this to. The original recipe called for another 1/2 recipe of frosting to allow for a crumb coat. I found that I didn't need it because the frosting went on so smooth that it didn't pull of any crumbs as I worked. You can find the original recipe at Martha's place.
2 white cake mixes (you need 6 cups of batter, each cake mix yields about 4 1/2 c.)
Mix cake mixes as directed on the box. (I used the egg white directions to keep the batter white to make the coloring process easier.) Grease and flour 9" rounds. Cut a piece of parchment to fit the bottom of each 9" round. Grease parchment paper and place in the pans. (You can use six disposable aluminum round pans or just bake in turns using regular 9" rounds.) Set aside. Using 6 separate bowl, place 1 cup of batter in each bowl. Color each bowl of batter (red, orange, yellow, green, blue and purple) with gel food coloring. Pour each cup of batter into an individual prepared pan and bake at 350 degrees for about 10 -12 minutes. Remove from oven and allow to cool on cooling rake for 5 -10 minutes before removing from pan. Allow each layer to cool completely, remove parchment paper from bottom the bottom, then wrap cake in plastic wrap to keep from drying out.
Lemony Swiss Meringue Frosting:
9 large egg whites
1 3/4 c. granulated sugar
2 c. (4 sticks) unsalted butter, cut into small pieces, room temperature
2 tsp. pure lemon extract
Cook egg whites and sugar in a small saucepan over medium heat, whisking constantly until sugar is completely dissolved. (This took me about 10-15 minutes) Transfer to the bowl of an electric mixer fitted with the whisk attachment; mix on high speed until mixture is near room temperature and soft peaks form. (You don't want the egg white mixture so warm that it melts the butter.) With the mixer on medium-low, add butter, one piece at a time, mixing well after each addition. Remove whisk attachment and switch to paddle attachment. Increase speed to high and beat until butter cream comes together, about 5 minutes; beat in lemon extract.
Begin laying the cake, starting with purple, cover each layer of cake with frosting before adding the next layer. Frost top and sides of cake. Refrigerate for at least 30 minutes before serving. Store covered in fridge.