This 2-Ingredient Chocolate-Peanut Butter Mousse Is Nothing Short of Magical

A Big Little Recipe has the smallest-possible ingredient list and big everything else: flavor, creativity, wow factor. Psst—we don't count water, salt, black pepper, and certain fats (specifically, 1/2 cup or less of olive oil, vegetable oil, and butter), since we're guessing you have those covered. Today, we’re making a two-ingredient mousse that just happens to be dairy-free.

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If I say mousse, you probably imagine something fluffy and airy and, above all else, creamy. But this chocolate–peanut butter mousse, though fluffy and airy, doesn’t have any cream. In fact, it only has chocolate and peanut butter.

Oh, and water. That’s our Big Little secret.

I first learned this magical technique years ago from Kristen Miglore’s Genius Recipes: “Hervé This, the father of molecular gastronomy, discovered how to make a flawless, creamy chocolate mousse out of just chocolate and water.”

It sounds like an impossible science experiment but, in reality, it’s as easy as melting chocolate and water on the stove, then whisking them over ice. Within a matter of minutes, the mixture goes from liquidy sauce to ethereal cloud.

As Kristen mentions, a dollop of whipped cream on top “is never a bad idea.” Because, while the chocolate mousse looks and feels and tastes decadent, it’s also bittersweet. A little fatty goodness goes a long way to balance it out.

The catch? Without that optional (but encouraged!) whipped cream, this Herve This’ mousse is dairy-free—and, depending on your chocolate of choice, vegan. Which is no small feat when dessert mousses so often rely on whipped cream or egg whites.

So, how can we add the aforementioned fatty goodness without adding dairy or eggs?

Just turn to another pantry staple: peanut butter. I don’t need to tell you that chocolate and peanut butter are a power couple. (Was Reese’s your favorite candy as a kid, too?) They’re great on their own and even greater together and, just like chocolate, peanut butter can be mousse-ified with nothing more than water and determination.

From a distance, this makes no sense. Water is a liquid, so it should make things more liquidy, right? But when it comes to ingredients like nut and seed butters, it does just the opposite. That’s why my Big Little Chocolatey Tahini Cups have a water-thickened tahini filling. And that’s why this peanut butter mousse is fluffy as can be, but still only one ingredient. As Cooks Illustrated explains with respect to tahini: “This is similar to what happens when chocolate seizes. A small amount of added water acts like a glue, wetting particles just enough to get them to stick together.”

The final surprise is in the assembly. If you try to swirl one mousse into the other (as I did many, many times), you get a chocolatey peanut butter mousse or a peanut buttery chocolate mousse, homogenous in color and muddled in flavor. If you layer the two together in a separate bowl—chocolate, peanut butter, chocolate, peanut butter—then scoop from there, you get distinct layers, and distinct flavors.

You can pop the mousse in the fridge, where it will thicken up, for later. But I find I can never wait that long.

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What’s your favorite way to make chocolate mousse? Tell us in the comments!