INGREDIENTS

1. Crust
   • 21 chocolate sandwich cookies (such as Oreos)
   • 1/4 cup (1/2 stick) unsalted butter, cut into pieces, room temperature
2. Mousse
   • 12 ounces semisweet chocolate, finely chopped
   • 1 teaspoon vanilla extract
   • Pinch of salt
   • 3 3/4 cups chilled whipping cream
   • 1/4 cup sugar
   • Chocolate shavings (optional)
     

     PREPARATION

     1. For Crust:
        1. Preheat oven to 350°F. Butter 9-inch-diameter springform pan with 2 3/4-inch-high sides. Finely grind cookies in 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 for 5 minutes. Transfer crust to rack and cool completely.
     2. For Mousse:
        1. Combine chocolate, vanilla, and salt in a processor. Bring 1 cup cream to boil in a heavy small saucepan. With processor running, gradually pour the hot cream through feed tube and process until chocolate is melted and smooth. Transfer mixture to a large bowl. Cool to room temperature, stirring occasionally.
        2. Beat 2 cups cream and sugar in a large bowl to stiff peaks. Fold into chocolate mixture. Pour mousse into prepared crust. Chill until set, about 6 hours. (Can be prepared 1 day ahead.)
        3. Beat remaining 3/4 cup cream in medium bowl to firm peaks. Transfer to a pastry bag fitted with a medium star tip. Pipe rosettes of cream around the edge of the cake. Garnish with chocolate shavings.