1. Mix the chocolate cookie crumbs with melted butter until evenly combined. Press the mixture firmly into the bottom of a 9-inch springform pan and chill for 20 minutes.

2. In a saucepan over medium heat, cook the raspberries, granulated sugar, lemon juice, and cornstarch until thickened and jammy. Let the raspberry mixture cool slightly, then spread it over the chilled crust. Return the pan to the refrigerator.

3. Beat the cream cheese until smooth. Add the powdered sugar, melted semi-sweet chocolate, vanilla extract, and salt, then mix until creamy and fully blended.

4. In a separate bowl, whip 1 1/2 cups of the heavy whipping cream until soft peaks form. Fold the whipped cream gently into the chocolate mixture until light and fluffy.

5. Spoon the mousse over the raspberry layer and smooth the top. Chill the cake for at least 4 hours, or until the mousse is firm.

6. Heat the remaining 1/2 cup heavy whipping cream until hot but not boiling. Pour it over the chopped semi-sweet chocolate and let it sit for 1 minute, then stir until smooth.

7. Cool the ganache slightly, then pour it over the chilled mousse layer. Let it spread naturally over the top.

8. Garnish with fresh raspberries and a mint sprig if desired. Chill for 30 minutes more before slicing and serving.