Mix cold espresso and rum in a small bowl. Mix in gelatin and let stand for 2 minutes.
3. Step
Add boiling water and stir until gelatin is completely dissolved.
4. Step
Mix sugar and cocoa in large bowl.
5. Step
Add whipping cream and vanilla. With an electric mixer, beat on medium speed until stiff.
6. Step
Pour in gelatin mixture and beat until well-blended.
7. Step
Add ½-inch (1.5 cm) layers of crushed cookies to dessert dishes, then scoop mousse into dishes and refrigerate for at least 30 minutes.
8. Step
While mousse is chilling, whip cream in a cold bowl until soft peaks form. Add mascarpone and powdered sugar and continue whipping until stiff peaks form.
9. Step
Scoop a dollop of whipped cream on top of the mousse and sprinkle with extra cocoa powder.
