Crush the graham crackers into fine crumbs and transfer to a mixing bowl. Pour in the melted butter and stir until the mixture resembles wet sand.
Press the crumb mixture evenly into a 23cm tart pan, creating a firm, level crust. Chill in the refrigerator for 10 minutes to set.
Meanwhile, melt the dark chocolate with 50g of butter using a double boiler or microwave in short bursts, stirring until smooth and glossy. Let it cool slightly.
Add the peanut butter to the melted chocolate and stir until fully combined. Set aside to cool a bit more.
Whip the chilled heavy cream in a mixing bowl until soft peaks form. Gently fold the whipped cream into the chocolate-peanut butter mixture, creating a smooth, airy filling.
Pour the filling into the prepared crust, spreading evenly with a spatula. Smooth the top for a clean finish.
Chill the tart in the refrigerator for at least 4 hours, or preferably overnight, until the filling is set and glossy.
Before serving, optionally decorate with chopped peanuts, a drizzle of melted chocolate, or a sprinkle of sea salt for extra flavor and visual appeal.
Use a warm knife to cut clean slices, wiping between cuts for neat presentation. Serve chilled or at room temperature for different textures.