1. Preheat the oven to 350°F. Lightly butter the bottom and sides of a 9-inch springform pan.
2. Combine the cookie crumbs and melted butter and press into the bottom of the springform pan. Bake for 10 minutes. Set aside to cool.
3. Over a double boiler, whisk together the yolks and 2 tablespoons of sugar until it is pale yellow and thick. Add espresso, Kahlua, and vanilla. Place over simmering water and whisk continuously and vigorously until liquid coats the back of a spoon and the mixture is thick and foamy.
4. Remove from the heat and add the chocolate. Stir until melted and continue stirring until cooled.
5. In a separate bowl, stir together the cream cheese and heavy cream until smooth. Do not overstir.
6. Place egg whites and 1/3 cup sugar in a mixing bowl. Gently whisk together over a simmering double boiler until it reaches 145°F. Remove from the heat and set the bowl on the mixer with the balloon whisk attachment. Whip on medium high until stiff peaks form. Reduce the speed to medium and mix until the bowl is cool to the touch.
7. Fold the cream cheese mixture into the chocolate mixture until there are no streaks left.
8. Fold ¼ of the meringue (egg white mixture) into the chocolate-cream cheese mixture. Fold in the remaining meringue in three parts. Do not overmix.
9. Spread the mixture over the baked crust in the pan. Tightly cover with plastic wrap and freeze for at least 4 hours.
10. When ready to serve, run a warm, dry knife around the sides of the pan, then loosen and remove the sides of the pan. Decorate with a drizzle of melted chocolate and fresh berries, if desired. Serve cold and cut slices with a warm, dry knife.