Chill your coconut milk overnight. In the morning, without shaking or tipping, remove the lid and scoop out the solid cream from the top into a chilled bowl. Leave the liquid in the bottom of the can and reserve it for use in smoothies, baked goods, etc. (If your coconut milk didn't harden, see this post for tips on how to save it.)
Using a mixer, beat until creamed together, light and fluffy - about 45 seconds.
Add peanut butter, starting with lower end of range (2 Tbsp as original recipe is written) and adding from there to desired taste.
Add sweetener of choice to desired sweetness, observing that the more liquid you add the less firm the mousse will be.
Either use immediately as a spreadable frosting, or chill for several hours to let it set and firm up as a mousse.
Eat as a mousse topped with plain coconut whipped cream, bananas or chocolate sauce. Alternatively, use as a dip for fruit/baked goods. If using as a frosting, don't frost your muffins, cookies and cakes, etc., until just before serving as it needs to be chilled right up until serving.
Reserve leftovers in a covered container in the fridge. Will keep for up to 1 week.
*You can sub 1/2 can coconut cream in place of the cream from 1 can coconut milk. *NOTE: Not all coconut milk is equal. The brands I know and recommend are Thai Kitchen, Trader Joe's (coconut cream, canned), and Whole Foods 365. Other brands source coconut milk from other regions of the world where the coconuts mysteriously have different fat make-ups, which can (and often do) affect the consistency of this mousse. *Nutrition information is a rough estimate. *Prep time does not include chilling coconut milk overnight.