*Before beginning, prep bowl and beaters by placing in the freezer for 15-20 minutes to chill.*
Sprinkle gelatin over cold water in small bowl; stir and let stand 1 minute to soften.
Add boiling water; stir until gelatin is completely dissolved. Let stand to cool.
Stir together sugar and cocoa in a large mixing bowl; add heavy cream.
Beat at medium-high speed until stiff peaks form; gradually pour in Baileys, vanilla, and gelatin mixture, beating continuously at high speed until well-blended and soft peaks form.
Let stand 5 minutes to thicken.
Spoon into serving dishes and place in refrigerator to chill. (*For a faster setting mousse, chill bowls before filling.)
Chill 1 hour or until ready to serve.