"[Photograph: Liz Gutman] This is more a technique than a recipe, but it's a lot of fun. It results in a light yet deeply chocolatey mousse that's totally vegan and dairy free. If you overwhip the first time around, it's easy to fix—just reheat, add a couple drops more water, and start over. This will keep for 2 to 3 days in the fridge...."