In the bowl of an electric mixer, beat the butter and sugar together until creamy.

Add the egg and mix it in.

Scrape down the sides of the bowl.

Sift in the flour, tumble in the oats and shake in the baking powder and salt and then mix them into the dough.

Carefully chop up the chocolate and add it to the bowl along with the lime zest.

Keep mixing until the dough comes together.

Tip it out onto a sheet of plastic wrap and roll it into a log shape 5cm thick, then wrap it up and refrigerate for at least 30 minutes.

Meanwhile, pre-heat the oven to 180C fan-forced.

Line two baking trays with baking paper.

Take the dough from the fridge and slice it up into 1cm thick discs then place them on the trays leaving at least 3cm between each one.

Bake for about 10 minutes or until they turn golden.

Leave the biscuits to sit on the tray for 5 minutes and then transfer them to a wire rack to cool completely.