Choose a chocolate that does not exceed 64% cacao for a mousse with the smoothest texture. If you want the mousse to be fully non-dairy, look for a vegan chocolate bar, though the flavor may differ slightly.
2 5-ounce cans coconut cream, chilled
7 ounces semisweet chocolate, coarsely chopped
½ cup aquafaba (the liquid strained from one 15-ounce can chickpeas)
¼ teaspoon cream of tartar
6 tablespoons coconut or light brown sugar, divided, plus more for serving
Six 4-ounce ramekins or one 7-inch ramekin
Open both cans of coconut cream and poke a hole into cream with a skewer or paring knife, going down to bottom of each can. The coconut cream will be a solid mass at top of can with a layer of coconut water suspended underneath. By poking a hole in the cream, you can drain off the separated coconut water. Pour out and discard (or drink!) all but 2 Tbsp. of the separated coconut liquid.
Heat chocolate, 2 Tbsp. coconut cream, and 2 Tbsp. separated coconut liquid in a medium heatproof bowl set over a small saucepan of barely simmering water, stirring occasionally, until melted and smooth. Chill remaining solid coconut cream until ready to serve.
Beat aquafaba, cream of tartar, and a pinch of salt in the bowl of a stand mixer fitted with the whisk attachment on medium-high speed until stiff peaks form and mixture is tripled in volume, 7–8 minutes. Add 3 Tbsp. coconut sugar, 1 Tbsp. at a time and scraping down sides of bowl if needed, and beat until no specks remain and mixture is homogenous, about 3 minutes more.
Remove bowl from stand mixer. Using large circular strokes and going in the same direction, gently fold about one-quarter of whipped aquafaba into chocolate mixture with a spatula until incorporated. Fold in remaining whipped aquafaba in 3 more additions until incorporated and no streaks remain.
Divide mousse among ramekins and chill until set, at least 2 hours (longer if you’re using a large ramekin).
Using an electric mixer on medium-high speed, beat reserved chilled coconut cream, 3 Tbsp. coconut sugar, and a pinch of salt in a medium chilled bowl until soft peaks form and no bits of coconut cream remain, 3–4 minutes.
Dollop mousse with whipped coconut cream and sprinkle with coconut sugar.
Do Ahead: Mousse and whipped coconut cream can be made 6 days ahead. Cover and keep chilled. You may need to beat the coconut cream to revive it.