Add the aquafaba to the bowl of your stand mixer and attach the whip. Add the cream of tartar or xanthium, and begin to whip at low speed for 2 minutes. Increase speed to medium and whip for 2 minutes more. Slowly add the sugar in a stream while whipping, and then turn the speed on high for 2 minutes. Check the mousse at this point, you should have nice stiff peaks. If not, whip it a little longer on high. Remove the bowl from the mixer.

Sift the peanut butter powder into the mousse. Carefully fold it in using a spatula. Spoon into glasses, then allow to set up in the refrigerator for at least a couple of hours. Best if eaten fairly quickly--the mousse will start to deflate after a day or so.