In a large heatproof bowl or the top pan of a double boiler, combine the chocolate, butter, coffee, and rum. Set over (not touching) barely simmering water and stir constantly until melted and smooth. Remove from the heat and let cool for 15 minutes.
Fold one-third of the whipped cream into the chocolate mixture to lighten it. Then fold in the remaining whipped cream just until combined. It’s better to have some streaks of cream in your mousse then to stir the mixture until it loses its airiness. Cover the mousse and refrigerate for at least 2 hours or up to 3 days.
In a stand mixer fitted with the whip attachment, combine 1 1/2 cups of the cream and the vanilla and whip on medium-high speed until soft peaks form. (Or, use a large bowl and a handheld mixer or a whisk.).
Line six half-pint jars with the crumb crust as directed in the recipe.
To line jars with the crust, spoon about 4 tablespoons of the crumb mixture into each jar. Take the jar in your nondominant hand (left hand if you are right-handed, for example) and start pressing the crumb mixture evenly into the bottom of the jar with your other hand. Now work some of the crumb mixture along the sides of the jar, pressing firmly. The crust should be about 1/4 inches thick and cover three-fourths of the jar. Fill the crusts immediately.
Whip the remaining 1/2 cup cream until soft peaks form. Spoon about 1/2 cup mousse into each crust-lined jar. Top with about 1 1/2 tablespoon of the ganache, then top the ganache with a dollop of the whipped cream. Alternatively, top the mousse with a dollop of the cream and grate or shave a little chocolate on top or dust with cocoa powder.
Serve immediately, or cover and refrigerate for up to 3 days. These pies can also be frozen for up to 1 month without the cream topping. Bring to room temperature and add the cream topping just before serving.
Chocolate Crumb Crust: In a bowl, combine the crumbs and butter and stir until the mixture is evenly moist.
Ganache Filling: Coarsely chop the chocolate by hand or in a food processor and place in a bowl.
In a small saucepan, heat the cream over medium heat just until bubbles form around the edges of the pan. Remove from the heat and pour over the chocolate. Let stand for 5 minutes, then stir with a wooden spoon until smooth. Stir in the butter until melted.
Let cool and use immediately or cover and refrigerate for up to 2 weeks.