01 -
Beat softened butter and powdered sugar in a bowl until smooth, about one minute. Mix in orange zest, vanilla and salt.
02 -
Sift flour and cocoa over the butter mixture. Mix on low speed or with a spoon just until clumps form, then press gently into a dough. Do not knead for a long time.
03 -
Shape into a log about 5 cm wide and 20 cm long. Wrap and refrigerate for 30 minutes, until firm enough to slice without squashing.
04 -
Heat the oven to 170°C / 340°F. Line two baking trays with parchment. Slice the dough into 20 rounds about 1 cm thick and space them apart on the trays.
05 -
Bake for 16–18 minutes until the edges are set and the surfaces look dry. Dark cocoa makes browning difficult to judge. Leave on the trays for 10 minutes, then transfer carefully to a rack and cool completely, about 20 minutes more.
06 -
Melt the dark chocolate in a heatproof bowl over a saucepan of barely simmering water, keeping the bowl clear of the water. Stir until smooth. Dip one half of each cooled cookie into chocolate, let excess drip off and lay on clean parchment. Allow the chocolate to set before stacking.
07 -
Store fully cooled cookies in an airtight container in a cool room for up to five days. Place parchment between layers. In a warm kitchen, refrigerate to keep the chocolate firm.