This is the second post in a series exploring the depths of egg yolks. For the basics of yolk science and some over-the-top deviled eggs, go here.
Picture this: it’s just after 8 on a Friday night (approaching 8:30 if we’re being honest, which I’m not), and the party I’m officially late for has begun a few miles away. The kitchen looks like a very chocolatey tornado blew threw it and I’m still deciding what to wear, but I actually feel pretty good. The mousse cups for tonight’s party are done, toppings and all, and the cake plus homemade nutella for tomorrow night’s party (I’m never this popular, I don’t know what happened) is cooling on the counter, safely out of reach of the kitten. Now I’m just a quick bus ride away and an hour isn’t really all that late, right?
Except apparently the bus isn’t running.
This throws me. It’s not too late, it’s not a holiday, there’s no crazy weather–what’s the deal? I consider a cab, but before I shell out an afternoon’s pay for what should be such an easy trip, my mind wanders into a dangerous trap I’ve encountered before. It goes like this:
I bet I could just take it on my bike.
Given that my bike is my primary mode of transportation, many a baked good has voyaged around the city in a backpack or strapped to my rear rack. I even took this cake, deconstructed, on a 10-mile journey to Evanston for a coworker’s birthday. But these are mousse cups, individual servings of chocolate goodness in a cupcake wrapper with a little cookie crust on the bottom, and chocolate mousse is not really known for its structural integrity. So they have to stay in the cupcake pan, and they have to stay upright. I throw the toppings in a bag, bungee the cupcake pan to the rack, and pedal off, easing gingerly over every bump and crack, into the potholed streets of Chicago.
It shouldn’t come as any surprise to you that this ended badly. I made it farther than I expected, but just when I thought I was going to pull it off, I heard a clatter behind me as the cupcake pan made a break for it. It wouldn’t cooperate in my attempts to get it back on the rack, so I gave up and walked the last mile or so. To rub it in, just as I reached my friend’s street and turned, two buses passed me in quick succession. Damn you, CTA!
This story has two morals. First, cupcake pans on a bike rack might not be the best idea. Second, even after a harrowing fall off of a moving vehicle and a close encounter with the road (the pan was covered, don’t worry), this mousse came through in a big way. With two kinds of chocolate and two ingredients whipped into airy foams, it’s somehow both decadent and delicate. It’s just the thing a person might need after a whirlwind baking session, an extremely stressful bike ride, and a long walk with a bike in one hand and a cupcake pan in the other. Theoretically, of course.
Before you whip out those double boilers and pump up your bike tires to set out on your own mousse-fueled adventure, let’s not forget that we’re smack in the middle of a series on egg yolks. I know I bashed mousse earlier for needing the support of a cupcake pan, but it actually holds itself together pretty well. And all of that structure comes from the humble egg yolk, playing one of its favorite roles as a stabilizing protein network.
You’ve seen the egg’s protein at work with your own eyes if you’ve ever cooked one. The liquid raw egg yolk gets gradually thicker as it heats (think an egg fried over medium), finally forming a solid mass once it hits about 158 degrees F (think fried egg with a broken yolk). If we looked more closely at the yolk during this transformation, we would see that the raw egg’s individually folded protein molecules start to unravel as the temperature rises. They stretch into long chains that then bump into each other and form new bonds and new structures with the other proteins, creating an interconnected web that holds together as a solid piece–the cooked yolk.
The yolk isn’t made of just protein, so the web of a fried egg forms around the water and other components of the yolk and holds them together, encompassing about one tablespoon total volume. By itself, the cooked product is firm and can be speared with a fork. But we’re not very good at leaving things alone, so we add all sorts of things to our egg yolks (and whole eggs, which we’ll use for easier examples–the protein network is pretty similar) and stretch them out. If we add just a little bit of liquid (a tablespoon of milk in scrambled eggs), the web has to expand around the extra liquid, making the cooked eggs softer than eggs cooked by themselves but still solid. If we add a whole lot of liquid (one egg in a pint of milk), the web can’t hold all of it in and the egg just works to thicken it, giving us something like eggnog. We’re going for something right in the middle: custards and creams are usually around a cup of liquid per egg for a semi-solid, pudding-like texture.
Mousse is a little bit different because the liquid here is mostly melted chocolate and butter, both solid at room temperature, rather than milk, but the idea is the same. The yolk proteins start to unfurl as we heat them, stretching out into long chains and forming the protein network that holds all of the yummy things (chocolate, butter, alcohol) together.
Made with two kinds of chocolate as well as both whipped egg whites and whipped cream, this mousse combines lightness and rich intensity for a chocolate experience like no other. I topped this with whipped cream and raspberries and it was just about perfect. If you want to make the mousse cups like I did the first time, make an easy cookie crust, press 1 T. of the crust mixture into the bottom of cupcake wrappers in a cupcake pan, and bake until golden brown. After you fold the whipped cream into your mousse, fill the wrappers the rest of the way with mousse.
8 oz. dark chocolate
4 oz. (1 stick) butter
2 T. cocoa powder
2 T. water
2 eggs plus 2 egg yolks
1/3 c. brown sugar
2 T. Triple Sec or other orange liqueur
½ t. vanilla
¼ t. salt
1 T. sugar
½ c. heavy cream
Heavy cream and raspberries, for topping
Heat about an inch of water in a medium pot. Combine the chocolate, butter, cocoa powder, and water in a heatproof bowl and place over the simmering water. Stir until the chocolate and butter are melted and the mixture is smooth. Remove bowl from heat and let cool.
Prepare a large bowl of ice water and set aside.
Whisk together the 4 egg yolks (reserve two whites), brown sugar, and Triple Sec in another heatproof bowl. Place over the pot of water and continue to whisk for about four minutes, until the mixture thickens and becomes lighter in color. Move the bowl to the ice water bath and keep whisking as the yolks cool. When you lift the whisk, it should leave a trail that you can see for a moment but that quickly fades back into the rest. Stir in the vanilla and heavy cream, and fold the chocolate mixture into the egg yolk mixture.
Whip the egg whites until frothy, then add the sugar and whip at high speed until medium peaks form. They should hold their shape, but peaks should fall slowly to the side rather than hold straight up.
Gently fold the egg whites into the chocolate mixture by thirds. Scoop 1/3 of the egg whites into the bowl with the chocolate, and get your spatula and your patience ready. With the blade vertical, draw the spatula through the center and scoop around the outside of the bowl, toward your body. Rotate the bowl a quarter turn and repeat. I know folding is slow, but stick with it! More vigorous stirring will pop the bubbles of your egg white foam and you need those to make your mousse super light and fluffy.
Whip the heavy cream to medium peaks and fold it into the chocolate just like you did the egg whites.
Transfer the mousse to individual bowls or a large serving dish and put it in the refrigerator to chill for at least 4 hours. Top with whipped cream (I like to sweeten it with about a tablespoon of powdered sugar and ½ teaspoon of vanilla for ½ cup heavy cream) and juicy raspberries.
Recipe adapted from The Science of Good Cooking from Cook’s Illustrated and David Lebowitz’s interpretation of Julia Child.