Prepare the Shortbread Dough:

In a medium-sized mixing bowl, beat together softened butter, powdered sugar, fine salt, vanilla extract, and orange zest (if using). Use an electric hand mixer or stand mixer with the paddle attachment to cream the mixture for about 3 minutes until pale and fluffy.

Sift cocoa powder and add half along with half of the flour to the butter mixture. Mix with a spatula until no dry ingredients remain. Add the remaining flour and cocoa powder, mixing until a soft, smooth dough forms. If the dough is too soft, refrigerate for 30 minutes to firm it up.

Baking Instructions (Scottish Style):

Preheat the oven to 150°C (300°F), or 130°C (265°F) if using a fan oven.

Grease and line a 22 cm x 31 cm (9 x 13-inch) baking dish with baking paper, leaving some overhang for easy removal.

Press the dough evenly into the dish. Use a flat cup or measuring cup to smooth out the surface.

Bake for 20 minutes. While the dough is still warm, cut it into 8 x 3 bars. Dock each bar with a fork 3 times and return to the oven for another 20 minutes until lightly golden.

Let the shortbread cool completely in the dish before gently separating the biscuits with a knife.

Alternative Shaping (Rectangular Biscuits):

Roll the dough into a log shape (about 20 cm in length, 6 cm in height) and chill it in the fridge for 1-2 hours.

After chilling, cut the dough log into 1 cm wide biscuits. Bake at 150°C (300°F) for 20 minutes, allowing them to cool completely.

Cookie Cutter Method:

Roll the dough into two flat discs between two pieces of baking paper. Chill the rolled dough in the fridge for 1 hour.

Preheat the oven to 150°C (300°F), or 130°C (265°F) with a fan. Use cookie cutters to cut out your desired shapes.

Bake for 20 minutes, and let the biscuits cool until firm.

Chocolate Coating (Optional):

Melt dark cooking chocolate and vegetable oil in a heatproof bowl using a microwave in 30-second intervals or by placing the bowl over simmering water. Stir until smooth.

Dip the cooled shortbread into the melted chocolate, allowing the excess to drip off. Place the coated biscuits on a baking tray lined with baking paper to set.