These shortbread biscuits have three stripes - an orange shortbread stripe, a chocolate shortbread centre stripe and a chocolate chip stripe. The result not only looks fabulous, but tastes delicious, too.
Combine the butter, sugar, egg and vanilla in a mixing bowl. Beat together by hand or at medium speed with an electric mixer, till smooth and creamy.
Add the flour and salt. Stir together till a dough forms. Divide dough into three equal portions.
Melt the cooking chocolate in the microwave, using short 10-second intervals until melted. Stir well, then add to one of the portions of dough and mix in thoroughly.
Mix the orange zest into the second portion of dough, then the finely chopped chocolate into the third.
Line a 900g loaf tin with cling film, leaving extra cling film overhanging from the edges. Press the orange zest dough into the bottom of the tin, then carefully press the chocolate dough over that. Finally, press the chocolate chip dough over top to create three layers. Cover and chill in the fridge for 2 hours or up to overnight.
Preheat the oven to 190 C / Gas 5 and line a baking tray with baking parchment.
Remove dough from the fridge and unwrap. Slice lengthways in half, then crossways into 5mm-thick slices. Place on prepared tin.
Bake in the preheated oven for 8 to 10 minutes, or till a light golden brown. Immediately remove from tray and transfer to a wire rack to cool.