Crust
21 Oreos
1/4 c unsalted butter, room temp, cut into pieces
Mousse
12 oz semisweet chocolate, finely chopped
1 tsp vanilla extract
1 pinch salt
3 3/4 c whipping cream, chilled
1/4 c sugar
chocolate shavings (optional)
For crust: Preheat oven to 350. Butter 9″ springform pan with 2 3/4″ high sides. Finely grind cookies in food processor. Add butter and process until mixture is evenly moistened. Press crumb mixture onto bottom and up sides of prepared pan to form a thin crust. Bake crust 5 minutes. Transfer crust to a rack and cool completely.
For Mousse: Combine chocolate, vanilla, and salt in processor. Bring 1 c cream to boil in heavy small saucepan. With processor running, gradually pour hot cream through the feed tube and process until chocolate is melted and smooth. Transfer mixture to a large bowl. Cool to room temperature, stirring occasionally.
Beat 2 cups cream and sugar in large bowl to stiff peaks. Fold into chocolate mixture. Pour mousse into prepared crust. Chill until set, about six hours. (Can be prepared 1 day ahead.)
Beat remaining 3/4 c cream in a medium bowl to firm peaks. Transfer to pastry bag fitted with medium star tip. Pipe rosettes of cream around edge of cake. Garnish with chocolate shavings.