1. Make mousse: Put chocolate in a large bowl, and set aside. Heat 1 1/2 cups cream over medium-high heat in a medium saucepan until cream is steaming and small bubbles form on edges.

2. Pour cream over chocolate. Stir until mixture is smooth. Let cool completely.

3. Put remaining 1 1/2 cups cream and the sugar in the bowl of an electric mixer fitted with the whisk attachment; beat on medium-high speed until stiff peaks form. Using a rubber spatula, fold whipped cream into chocolate mixture, one-third at a time.

4. Assemble torte: Line a 9-by-5-by-3-inch loaf pan with plastic wrap, leaving an overhang on sides. Spread enough mousse (3/4 to 1 cup) over bottom of pan to cover. Arrange 5 cookies on top in a single layer to cover, breaking them to fit as necessary. Spread enough mousse (3/4 to 1 cup) on top to cover; smooth into an even layer. Repeat process with remaining cookies and mousse until pan is full.

5. Press plastic wrap directly onto surface, and refrigerate torte until firm, at least 3 hours or up to 2 days.

6. Remove plastic wrap from surface. Invert torte onto a serving plate; unmold, using overhang to coax it out. Remove plastic wrap. Dust with cocoa.