Mix Kahlua with water in a large saucepan; sprinkle gelatin over top and let stand 1 minute.
Stir over low heat until gelatin is completely dissolved, about 3 minutes.
Add chocolate; stir until melted and smooth.
Remove from heat; whisk in egg yolks one at a time. Cool to room temperature.
In large bowl, beat egg whites with electric mixer until soft peaks form when beaters are lifted. Gradually add sugar; beat until stiff glossy peaks form.
Stir a largo dollop of whites into the chocolate mixture until blended, then fold the chocolate mixture into remaining whites.
Whip the cream and fold it gently into the chocolate mixture.
Spoon some mousse mixture into an 8 or 8-1/2 inch springform pan to make a 1/4 inch layer. Stand cookies in the mousse all around the inside edge of the pan, using the mousse to glue the cookies together. Gently pour in the remaining mousse.
Cover loosely with waxed paper and chill at least 3 hours until firm, or overnight.
To serve, remove sides from springform pan. With sharp knife, cut into servings 2 cookies wide.