Classic White Layer Cake with Chocolate Buttercream Frosting

For my friend's birthday, I made him a traditional white layer cake with a chocolate buttercream frosting, and it turned out great so I figured I would share it. I got the cake recipe from Baking Illustrated from the Cook's Illustrated people and the chocolate buttercream was adapted from A World of Baking by Dolores Casella. Since he is a big Green Day fan, I re-created the cover of American Idiot with powdered sugar and red frosting. Here we go. (Note: t = teaspoon, T=tablespoon)

Cake:
2 1/4c. Flour (all-purpose or cake)
1 c. milk (room temperature)
6 large egg whites (room temperature)
2 t. almond extract
1 t. vanilla extract
1 3/4c. granulated sugar
4 t. baking powder
1 t. salt
12 T. unsalted butter (softened, but cool)

1. Preheat the oven to 350 and grease your 9-inch cake pan(s).
2. Mix the egg whites, milk, and extracts in a bowl or 2-cup measuring cup.
It will look something like this:

3. Mix flour, sugar, baking powder, and salt in a mixing bowl. I recommend finding aluminum-free baking powder like Rumford's:

4. Add butter to flour mixture and mix well until the mixture resembles fine crumbs.
It should look like this:

5. Add all but 1/2 cup of the milk mixture and beat 90 seconds in a stand mixer or 120 seconds with a hand-held mixer. Scrape the sides of the bowl and add the remaining milk mixture and beat another 20 seconds. It should look like this:

6. Divide the batter evenly into the cake pans. If you only have one one cake pan, scoop about 3 cups into the pan, as the mixture totals about 6 cups. Make sure you spread the batter to the edges of the pan and smooth the top. Bake until you can stick a toothpick in and it comes out clean, about 22-25 minutes. They will look like this:

7. Let them sit in the pan for a few minutes then invert on a rack or a clean surface. Make sure you are gentle with them, as they have a tendency to break apart if not fully supported. Let cool fully (about 1 hour). Then you are ready to make the frosting.

Frosting:

3/4 c. softened butter (or margarine)
2 3/4 c. powdered sugar
1 large egg or 2 egg yolks (the yolks make it a bit richer)
Generous 1/3 c. baking cocoa or 3 squares of melted unsweetened chocolate
1 t. vanilla extract or rum or whatever flavoring you would like
1/4-1/2c. half & half or cream (optional)

1. Cream the butter or margarine. It will look like this:

2. Add powdered sugar and mix thoroughly.
3. Beat in the egg, chocolate or cocoa, and flavoring.
4. If you want it thinner, add some half and half or cream.

The frosting should look like this:


Now, time to frost it up!

1. Place the first layer upside-down on your serving surface.
2. Put a large dollop of frosting on the top (bottom) of the first layer and spread it out to the edges.
3. Place the other layer on top (again, upside down) and dollop a good amount of frosting on top and spread it to the edges. Like so:

4. Now, scooping out a little frosting at a time, spread the frosting on the sides of the cake, making sure that is it is totally "sealed." Smooth the frosting out, and if desired, go over it with a hair dryer on hot to give it that glossy, professional look. Here is the undecorated cake and the final presentation with the cover art on it: