Combine graham cracker crumbs with melted butter in a bowl and stir until the crumbs are evenly coated and moist.
Press this mixture firmly into the bottom and sides of a 23cm tart pan to create an even crust. Bake in a preheated oven at 180°C (350°F) for 12-15 minutes until golden and fragrant.
While the crust bakes, melt the chopped dark chocolate gently in a double boiler or microwave, stirring every 30 seconds until smooth and glossy.
In a bowl, warm the peanut butter slightly to loosen it up, then fold it into the melted chocolate until fully combined and smooth.
Pour the chocolate-peanut butter mixture over the cooled crust, using a spatula to spread it evenly and smooth out the surface.
Place the tart in the refrigerator and chill for at least 4 hours, or overnight, until the filling is firm and glossy.
Before serving, sprinkle chopped peanuts on top or drizzle with melted chocolate for extra texture and flavor.