Preheat oven to 350 degrees. Make the chocolate crust: Combine cookie crumbs, granulated sugar, and 1/4 teaspoon salt in a bowl. Stir in butter. Press mixture into bottom and 2 1/2 inches up sides of 9-inch springform pan. Bake until dry and firm, 8 to 10 minutes. Let cool.

2. Make the caramel sauce: Heat granulated sugar and water in a medium saucepan over medium-high heat, washing down sides of pan with a wet pastry brush to prevent sugar crystals from forming, until medium amber, about 10 minutes. Remove from heat, and carefully add heavy cream (mixture will bubble and steam). Return to heat, and bring to a boil, making sure caramel that seized up when cream was added melts. Transfer to a bowl, and stir in creme fraiche. Refrigerate until cool but still pourable, about 45 minutes. Fold in peanuts.

3. Meanwhile, make the peanut butter mousse: Beat cream cheese and confectioners’ sugar with a mixer on medium-high speed until pale and fluffy. Beat in 1/2 teaspoon salt. Add peanut butter and vanilla, and beat until combined. Whisk heavy cream in a separate bowl until medium-stiff peaks form. Fold one-third of the whipped cream into peanut butter mixture. Fold in remaining whipped cream in 2 additions.

4. Assemble the tart: Pour caramel sauce into cooled chocolate crust. Gently spread peanut butter mousse over caramel in an even layer, making sure they don’t blend together. Refrigerate for 30 minutes.

5. Make the chocolate ganache: Place chocolate in a small heatproof bowl. Bring cream to a simmer in a small saucepan over medium-high heat. Pour cream over chocolate, and let stand for 1 minute. Whisk to combine. (Use immediately.) Remove tart from refrigerator, and pour in ganache to cover surface. Refrigerate for at least 30 minutes.