Break up the cookies into small pieces using a food processor or a zip top bag and mallet.
In a medium mixing bowl, combine the crushed cookies and melted butter using a fork. Press the cookie mixture into the bottome of a 9-inch pie pan. Place in the oven to bake for 10 minutes. Remove and set aside to cool.
For Flourless Chocolate Cake: Raise oven temperature to 350°F.
Over a double boiler, melt chocolate chips with butter, and stir to combine. Remove from heat. Add the coffee, vanilla and salt, and stir to combine. Set aside to cool.
In a separate bowl, add 6 egg yolks with one cup of sugar, and mix until combined.
Add the chocolate mixture to egg mixture.
In a large bowl, whisk whites to soft peaks. Then, fold the whipped egg whites into the chocolate mixture.
Transfer chocolate mixture into the baked and cooled crust.
Place in the oven to bake for 35 minutes.
Remove from the oven and let cool completely. (The cake mixture will fall, making space for the mousse to sit on top.)
For Chocolate Mousse: Meanwhile, combine the chocolate chips, coffee, butter and rum in a double boiler. Stir to melt and combine.
Pour the whipping cream into the bowl of a stand mixer, and place both in the refrigerator to chill.
In a separate bowl, add gelatin and cover with a 1/4 cup of the chilled whipping cream. Place this bowl over indirect heat, just enough to melt the gelatin.
Let gelatin cool off.
Add the gelatin mixture to chocolate, and fold in. Beat the remaining cold whipping cream to medium peaks. Fold the whipped cream into the chocolate.
For Assembly: Place mousse mixture on top of cooled flourless cake. (Feel free using your hand to push down the cake to make room for mouse to sit.)