Place graham crackers in the bowl of a food processor, and pulse until fine crumbs are formed. Transfer to a medium bowl, and add butter. Stir with a fork until thoroughly combined. Place crumbs in a 13 3/4-by-4 1/4-inch rectangular tart pan with a removable bottom. Press crumbs up the sides of the pan to form the edge of the tart and then evenly over the bottom of the pan. Place in the refrigerator while making the filling.
Fill a large bowl with ice and water. Finely chop chocolate, and place in a medium bowl. Place 1/2 cup cream in a small saucepan over medium heat, and bring to a boil. Pour over chopped chocolate, and set aside for 5 minutes to yield chocolate ganache. Whisk to combine. Set in ice bath until ganache is cool, whisking constantly. Once cool, remove from ice bath, and whisk until ganache is just thick enough to hold its shape; do not overbeat. Spread in the bottom of the prepared crust, and return to the refrigerator until set.
Combine peanut butter, cream cheese, and sweetened condensed milk in the bowl of a food processor; process until smooth. Transfer to a mixing bowl.
Whip 3/4 cup heavy cream to soft peaks. Add whipped cream to peanut butter mixture; whisk to combine.
Spoon mixture into prepared crust; return to the refrigerator for 2 hours or overnight. Remove tart from refrigerator, and transfer to a serving platter 10 minutes before serving. Whip remaining 1/2 cup cream. Top tart with dollops of whipped cream. Use a vegetable peeler to make chocolate curls for garnish.