Mix the flour and powdered sugar in a bowl, then cut in the softened butter until the mixture resembles coarse crumbs. Press this dough evenly into the bottom of your tart pan, making sure to create a rustic, slightly uneven edge. Bake in a preheated oven at 180°C (350°F) for about 15 minutes until golden and fragrant. Let the crust cool on a rack.
Place the chopped dark chocolate in a heatproof bowl. In a small saucepan, heat the cream just until it begins to simmer, then pour it over the chocolate. Let sit for a minute, then stir gently until smooth and glossy. This creates a rich chocolate ganache.
Stir the peanut butter into the warm chocolate ganache until fully combined and silky. The mixture should be smooth and thick, with a luscious sheen. Pour this filling into the cooled crust and spread evenly with a spatula.
Place the tart in the refrigerator and chill for at least 2 hours, or until the filling is firm and shiny. This step helps the flavors meld and the filling set perfectly.
Once chilled, optionally sprinkle chopped peanuts on top for added crunch and visual appeal. Slice the tart with a heated knife for clean, neat pieces. Serve straight from the fridge for the ultimate gooey, satisfying bite.