Cream softened unsalted butter and powdered sugar until pale and fluffy, about 3 minutes.

Mix in fine salt, vanilla extract, and optional orange zest until combined.

Gradually sift in all-purpose flour and cocoa powder while mixing at low speed until a crumbly dough forms.

Knead the dough gently to form a smooth texture that is easy to shape.

If too soft, wrap the dough in plastic wrap and refrigerate for 30 minutes.

Preheat oven to 150°C (300°F). Press the dough into a lined 8x8 inch baking tin and bake for 20 minutes.

Cut shortbread into bars while warm, then dock the center with a fork and bake for another 20 minutes.

Alternatively, shape into a 2 inch wide log, chill for 1-2 hours, then slice and bake until golden.

For cookie shapes, roll between parchment sheets to ¼ inch thick, cut shapes, and bake until edges are firm.

Cool in tin for 10-15 minutes, then transfer to a wire rack to cool completely.

Melt dark chocolate with vegetable oil and dip or drizzle over cooled biscuits.

Allow dipped biscuits to set on parchment paper.