Crush the cookies into fine crumbs and transfer to a mixing bowl. Mix in the melted butter until the crumbs are evenly coated and resemble wet sand.
Press this mixture firmly into the bottom and up the sides of a tart pan with a removable bottom, creating an even crust. Use the back of a spoon or your fingers to smooth the surface.
Bake the crust in a preheated oven at 180°C (350°F) for about 10 minutes until golden and fragrant. Remove from the oven and let it cool slightly to set.
Meanwhile, melt the chopped dark chocolate and 100g of butter together using a double boiler or microwave in short bursts, stirring until smooth and glossy. Smell the rich cocoa aroma as it melts.
Add the creamy peanut butter to the melted chocolate mixture and stir until fully combined, creating a luscious, thick filling. The mixture should be glossy and smooth.
Pour the chocolate-peanut butter filling into the cooled crust, spreading it evenly with a spatula. The filling will be thick and gooey.
Place the tart in the fridge and chill for at least 4 hours or overnight to allow the filling to set and develop flavor. The top should look glossy and firm when ready.
Just before serving, optionally melt a little more chocolate to drizzle over the top or sprinkle chopped peanuts for added texture. Let the tart sit at room temperature for about 10 minutes to soften slightly for the best bite.
Slice with a warm knife, wiping it clean between cuts to achieve neat pieces. Serve and enjoy the rich, gooey mess that’s full of flavor and imperfect charm.