Pulse the graham crackers in a food processor until they turn into fine crumbs, releasing a buttery aroma.
Mix the crumbs with melted butter until the mixture resembles damp sand and holds together when pressed.
Press the crumb mixture evenly into the bottom and up the sides of a tart pan with a removable bottom, creating a compact crust.
Bake the crust in a preheated oven at 180°C (350°F) for about 10 minutes until golden and fragrant, then remove and let cool slightly.
Meanwhile, melt the finely chopped dark chocolate gently over a double boiler or in short bursts in the microwave, stirring until smooth and glossy.
Stir the peanut butter into the melted chocolate until fully incorporated, then add powdered sugar if desired, mixing until smooth.
Pour the chocolate-peanut butter filling over the cooled crust, spreading it into an even layer with a spatula.
Place the tart in the fridge and chill for at least 2 hours until the filling is firm and glossy.
Once set, carefully remove the tart from the pan, slice with a warm knife, and serve with optional toppings like chopped peanuts or toasted coconut.