Egg whites are back! To finish out the series I started before I took that whole gluten and dairy break, I’ve got one more piece of the science and a home-run recipe for you. To learn more about how egg foams work and how to use whipped egg whites in all sorts of yummy desserts, check out the earlier posts: meringues, a pavlova, and your very own marshmallow fluff.
These cupcakes with the longest name ever are also known as birthday cupcakes for the baby. And before you give me any grief about giving all sorts of refined sugar and whatever else to an infant, the baby in question is my little sister, who is 19. I guess nicknames are the price you pay for being the spoiled youngest.
The baby came out to Chicago to visit for a few days on her way home from college, so obviously we had to bake together. It had been her birthday the week before–smack dab in the middle of finals. No good. And no cake, which is unacceptable. Having hooked her on the idea of peanut butter cream cheese frosting, we built these cupcakes around that topping. The end result is a sweet, springy yellow cupcake topped with plenty of frosting, and of course some ganache to round it out because you can’t have a birthday in my house without chocolate.
I can’t tell you enough how great this frosting is. For something based on peanut butter and cream cheese, both pretty heavy, it’s amazingly light and fluffy. If you’re skeptical about the flavor combination, I’m not sure we can be friends. The tang of the cream cheese balances the peanut butter perfectly–seriously, this stuff is addictive. And the rest of the cupcake isn’t too shabby either. A basic yellow cupcake gets a lift from browned butter and whipped egg whites, and the chocolate ganache makes the whole thing super decadent. It’s the perfect treat to celebrate someone special. And don’t forget–if it’s their birthday, they get to lick all of the spoons.
We’ve talked a lot about whipping egg whites and how the proteins create a matrix that makes this beautiful, delicate foam. That’s great and all, but we really need to heat them up to give them any sort of useful lifetime. You may have seen meringue pies that “weep,” and it’s not because they’re really upset that you’re about to cut them into pieces and shove them into your mouth. The egg proteins form a scaffolding for the foam, holding together the liquid from the whites and the air bubbles that make it so fluffy. But the overconfident proteins think they’re much stronger than they are, so as time goes on they lose their grip on each other, the mesh gets some holes in it, and you see liquid puddling out of the meringue.
The heat sets the proteins in place through coagulation, something you know about if you’ve ever fried an egg. Think about the white through that process: it starts out basically clear and liquid, then gradually turns opaque white and solid as it cooks. As the proteins get hot, they unravel (we call it denaturing) and get all tangled up together in what we see as the solid white. If you’ve been paying attention, you’ll realize that creating the egg foam also relies on denaturing proteins–what does the heat bring that the whipping doesn’t?
It’s really all about just one protein, ovalbumin. It makes about half of the egg white proteins and, significantly, doesn’t respond to whipping. This means that when you whip egg whites, you make a foam with the rest of the proteins while ovalbumin hangs around and does nothing, much too cool to join the protein scaffold. Stick the foam in the oven, though, and you’ll get this wallflower to join the party. It coagulates around 180 degrees F, so when the foam hits that point, it gets a huge boost in structural integrity as all of that ovalbumin denatures and adds stability. With the heat also evaporating water from between the proteins, baking egg foams really firms them up and allows you to keep them for a day or two (like marshmallow fluff) or even much longer (like meringue cookies).
Yellow cupcakes with peanut butter cream cheese frosting and chocolate ganache
This ideal special-occasion cupcake combines all of my favorite flavors while remaining perfectly light and fluffy. The peanut butter cream cheese frosting melts in your mouth, the cupcake brings a delicate sweetness, and the chocolate ganache pulls it all together. Whipped egg whites are folded in at the very end of the cupcake, giving it an extra airy boost.
Yield: 24 cupcakes
6 T. butter
6 eggs, separated
1 c. white sugar, separated
2 T. vegetable oil (or other neutral oil)
1 c. buttermilk
1 T. vanilla
1 ¾ c. + 2 T. flour
2 T. cornstarch
½ c. brown sugar
¼ t. baking soda
¾ t. baking powder
½ t. salt
Peanut butter cream cheese frosting
1 c. creamy peanut butter
5 oz. cream cheese, room temperature
4 oz. (1 stick) butter, room temperature
2 c. powdered sugar
¾ t. salt
¼ c. heavy cream
2/3 c. dark chocolate chips or 4 oz. dark chocolate, chopped
Yellow cupcakes: preheat the oven to 350 degrees F. Line 24 cupcake wells with paper liners or grease them well.
To brown the butter, place it in a small pot over medium heat until it melts, bubbles, and has brown flecks on the bottom. It will start to smell nutty and delicious when it is done. Let cool.
Whip 4 egg whites with an electric mixer at medium speed until bubbly. Slowly add ¼ c. white sugar and whip at high speed until medium peaks form. The tips should fall slightly when you lift the whisk but should not form a closed loop.
Combine the browned butter, oil, buttermilk, 2 whole eggs, 2 egg yolks, and vanilla in a large bowl. Mix together.
In a separate bowl, mix all of the dry ingredients. Stir the flour mixture into the butter mixture just until combined. Gently fold in the egg whites in three parts.
Fill prepared pans with cupcake batter, filling each well about ¾ full. Bake for 15-18 minutes, until the top of the dome feels firm and springs back when you touch it.
Peanut butter cream cheese frosting: with the paddle attachment of a stand mixer or an electric beater, beat the peanut butter, cream cheese, and butter until combined and light in color, about 1 minute at high speed. Add the powdered sugar and salt and beat on low speed until combined. Beat at high speed for an additional 30 seconds. Transfer to a pastry bag (you can use a decorative tip if you want, I just cut the tip off of my bag).
Chocolate ganache: heat the cream in the microwave or over gentle heat. When hot, add the chocolate and stir constantly until the chocolate melts and the mixture is smooth. Let cool.
Assemble the cupcakes: spread a layer of ganache on the top of the cupcake. Pipe a spiral of frosting over the ganache, leaving a ring of chocolate visible on the outside. Give to your favorite birthday girl and enjoy together!
Cupcake recipe adapted from Smitten Kitchen and The Science of Good Cooking from Cook’s Illustrated. Science, as usual, from McGee.