Many years ago, I had a recipe for pareve ice cream that was perfect, except for one thing: it called for raw eggs. I revised the recipe a while back by heating the eggs with sugar until they reached a safe temperature. But, that was kind of a pain to do.
Now, I have veganized that recipe, replacing the eggs with something that has recently been dubbed aquafaba, a neologism for the liquid left over from cooking beans. It seems that this liquid can be whipped into something very much like meringue. It can be turned into meringue cookies, topping for lemon meringue pie, marshmallows, marshmallow fluff, Italian meringue buttercream and more . . .
In the last several months, there has been a flurry of experimentation with this in the vegan community. It seems to have started with Jöel Roessel, who discovered that the liquid from cooked chickpeas could be whipped into meringue and then posted about it on his blog, Revolution Vegetale. It really took off, though, when Goose Wohlt shared his experimentation with this technique via Facebook (full story here and here and here). There is much more information on this Facebook page.
Theoretically, all you need to do for aquafaba mousse is whip the liquid from a can of chickpeas until it forms a dense white foam and then fold into the foam some melted chocolate (3.5 ounces). I think that the mousse has better texture when sugar is whipped into the aquafaba foam. The added sugar makes for a dense, stable meringue instead of a delicate foam. To balance the added sugar, I add in some cocoa powder and oil.
I have tried this mousse various ways. I am giving you two versions I especially liked. The first version has more sugar/cocoa/oil. The meringue is especially stable, but the resulting mousse is very light and delicate instead of dense and firm. If you like a denser, firmer mousse, try the second version, which adds in more chocolate and reduces the cocoa/sugar/oil.