Crust:
Microwave peanut butter and butter in a medium bowl until melted.
Beat butter into peanut butter until well combined.
Stir in vanilla, beaten eggs, and sweetener.
Add the rest of the ingredients and stir until dough forms.
Press dough into a 9-inch pie pan. Use the tines of a fork to poke holes throughout the crust to prevent puffing up while baking. Bake at 325°F for 15-20 minutes.
Place on rack to cool.

Mousse Filling:
Sprinkle gelatin over cold water in a small bowl; let stand 2 minutes to soften.
Add boiling water; stir until gelatin is completely dissolved and mixture is clear.
Cool slightly.
Combine sweetener and cocoa in a large bowl; add whipping cream and vanilla.
Beat on medium speed of mixer, scraping bottom of bowl occasionally, until mixture is stiff.
Pour in gelatin mixture; beat until well blended.
Spoon into pie crust. Refrigerate at least 4 hours before serving.