Blend together all the ingredients in a large bowl for the mousse using a blender.
Once the mixture is fully blended, pour the mousse into a cup. Place this in the refrigerator for at least one hour, until thickened.
If making the chocolate layer, add the chocolate with a splash of water if needed, in a small saucepan.
Fill a larger saucepan with water, and place this on the stovetop over medium-low heat.
Place the smaller saucepan with the chocolate on top of the larger one. This creates a "double boiler" method at home, and avoids the chocolate clumping when it melts.
Constantly stir the chocolate with a whisk or spatula to melt.
Once melted, remove the saucepans from the stovetop. Pour the chocolate mixture over the refrigerated peanut butter mousse in the cup.
Refrigerate for an hour or two, until the chocolate shell is hardened.
When serving, top with optional vegan whipped cream, if desired. Enjoy!