Here is the source I "blog lifted" this beautiful cake and recipe from :) Thoughts of Creativity Bubbling Over, a blog that I follow and am inspired by regularly!
Rainbow Cake
White Cake
2 sticks (226 g) butter, room temp
2 1/3 c (466 g) sugar
5 egg whites, room temp
2 teaspoons vanilla
3 c (375 g) flour
4 tsp baking powder
½ tsp salt
1 1/2 c (355 g) milk, warmed for 30 sec in microwave to bring to room temp
Red, orange, yellow, green, blue and purple GEL food coloring. Liquid will not be vibrant enough!
Preheat the oven to 350F degrees. Oil and line how ever many 9” cake pans you have (I have three and I just reused them).
Sift together the flour, baking powder and salt. Set aside.
Cream the sugar and butter, then add the egg whites (I cracked them all into one bowl) and add them a little at a time. Add the vanilla and mix until fully incorporated. Then, alternating between wet and dry, add the milk and flour mixture in two parts.
Divide the batter amongst 6 bowls (I did it by weight. Weigh your mixing bowl before you begin adding ingredients and then subtract the weight of the bowl from the final measurement after the batter is completed. Divide that number by six and add that weight of batter to each bowl), and then whisk a fair amount of the appropriate food color into each bowl. Pour into the pans and bake for 15 minutes each.
When you remove them from the oven, let them rest on the cooling rack, in the pan, for ten minutes. Then flip, cover, and stash them in the fridge to cool quickly.
Lemony Swiss Meringue Buttercream
To fill and crumb coat:
9 egg whites
1 ¾ c (350 g) sugar
4 sticks (532 g) of butter, room temp
2 tsp lemon extract
To frost:
5 egg whites
1 c (200 g) sugar
2 sticks (226 g) butter, room temp
1 tsp lemon extract
Cook the egg whites and sugar in a small saucepan over medium heat, whisking constantly, until the sugar is completely dissolved (test by rubbing some between your fingers. If it's completely smooth, it's done). Pour into another bowl (a stand mixer is preferable) and whip on high speed until room temp. Then, on a medium-slow speed, add the butter, waiting until each piece is completely incorporated before adding the next. After all the butter has been added, turn the mixer back to high speed and whip until it has come together, about five minutes. Add the extract, beat briefly and then use.
If the buttercream seems soupy after all of the butter is added and does not come together after whipping, refrigerate for 5 to 7 minutes and continue whipping until it becomes fluffy and workable.
