Preheat the oven to 190°C/375°F/gas 5.

Grease a 20cm square baking tin and line with greaseproof paper.

In a bowl, mix together the butter, flour, sugar and the finely grated zest of half the orange by rubbing the mixture between your thumbs and fingertips.

Squash and pat into dough – don’t knead it – then push into the lined tin in a 1cm-thick layer.

Prick all over with a fork, then bake for 20 minutes, or until lightly golden.

Remove, sprinkle over a little extra sugar while it’s still warm, then leave to cool.

Meanwhile, melt the chocolate in a heatproof bowl over a pan of gently simmering water, then remove.

Cut the shortbread into 12 finger portions, then transfer to a wire cooling rack.

Drizzle with the chocolate, then finely grate over the remaining orange zest.

Cut up the orange, and serve on the side!