In a small microwavable bowl, boil water by microwaving for about 1-2 minutes or until bubbling.
Shake in gelatin powder and whisk until dissolved. Put bowl in fridge to cool it down.*
In a large bowl, whisk together cocoa powder and sugar until combined. Add heavy cream then beat using a hand mixer until stiff peaks form.
Add cooled* gelatin water then add raspberry jam and vanilla. Beat together until thoroughly combined. *Make sure gelatin water has significantly cooled. If it's too warm, this could cause the mousse not to thicken or stay whipped.
Spoon mousse into 4 ramekins, smoothing over the top.
Refrigerate for at least 2 hours then top with raspberries and mint leaves right before serving.