Using a handheld or stand mixer fitted with the paddle attachment, beat the butter and icing sugar until smooth and creamy. Add the egg, and orange juice, and beat until combined.

Add the flour, orange zest, and salt, and beat until combined. Add more flour if dough is too sticky to handle.

Turn the dough out onto a lightly floured surface and shape into a 12-inch long log, or two 6-inch logs.

Tightly wrap the log in clingfilm and refrigerate for at least 4 hours, and up to 5 days. I like to chill mine overnight.

Preheat the oven to 180C/350F/Gas 4, and line a baking tray with parchment paper or a silicone mat. Set aside.

Slice the log into thick slices, and place them onto the prepared baking tray. Bake for 10 - 12 minutes until lightly brown around the edges.

Allow to cool for 5 minutes before transferring them to a wire rack to cool completely.

Add the chocolate to a microwave-safe bowl, and heat in 20 second intervals, stirring after each one, until melted and smooth.

Dip each cooled cookie in the melted chocolate, and leave to set on a baking tray lined with parchment paper. You can refrigerate to set the chocolate more quickly.