Now you need to work quickly, as the dough must stay as cold as possible. It's best to first rub the mixture together into a crumbly texture, then add the egg yolk.

Again, work quickly to form a smooth, soft dough. I recommend using a stand mixer, as it won't warm the dough up. Wrap the dough in plastic wrap and chill in the fridge for at least 1 hour, ideally overnight.

Before baking, line your baking trays with parchment paper. Preheat the oven to 150 °C (fan) or 160 °C (top and bottom heat).

Roll out the dough on a lightly floured surface and cut out the shapes – always one whole piece and one with a cut-out centre to match. Bake for 12 minutes, keeping an eye on them so they don't get too dark. They should stay light in colour.

Once the cookies have cooled slightly on the tray, carefully transfer them to a wire rack to cool completely.

Beat the softened butter with the sugar and hazelnut cream until smooth. Dip the cut-out tops halfway into melted chocolate and sprinkle lightly with chopped pistachios.

Once the chocolate has set, spread the cream on the plain bottom halves and sandwich the two pieces together.