For Crust:
Combine cookie crumbs and melted butter. Press firmly into bottom and partially up sides of springform pan with parchment-lined base.
For Mousse Filling:
Gently melt chocolate in top of double boiler over simmering water. Let cool 15 minutes but not longer. (chocolate too warm= syrupy, chocolate too cold= graininess, try to make ingredients same temp)
While chocolate cools, in a large bowl, beat egg whites until soft peaks form; gradually beat in sugar, then beat on high 1-2 minutes longer, until meringue thickens and becomes glossy.
Set aside.
In another bowl, whip cream until peaks form; refrigerate.
Whisk egg yolks with a little cream; then, as fast as possible, beat into the cooling chocolate; it will clump to beaters and be glossy.
Transfer chocolate to the meringue bowl and beat on low until uniform, then add whipped cream and mix with beaters just until well incorporated.
Turn into prepared crust.
Cover and chill 4-6 hours till firm.