Preheat oven to 325 degrees F. Dissolve the coffee in the vanilla extract and set aside.
In a small bowl, mix the graham cracker crumbs, cocoa, 2 tablespoons sugar, and melted margarine. Press into the bottom of a 9-inch spring form pan.
In a large mixing bowl, mix both of the cream cheeses, flour, cornstarch, remaining 8 tablespoons (1/2 cup) sugar, egg, and the coffee dissolved in vanilla, beating until well mixed.
Add the sour cream and milk, mixing well. In a separate bowl, beat the egg whites until stiff, gradually adding the remaining 4 tablespoons (1/4 cup) sugar, and fold into the cream cheese mixture. Pour the mixture over the crust in the spring form pan, and bake for 1 hour.
Leave in the oven with the door slightly open for 1 more hour, and refrigerate for at least 2 hours before serving.