Put all the ingredients in a food processor and whizz until they come together into a dough: don't be tempted to add water, just keep processing until you have a smooth ball of dough.

Making by hand: stir together the ingredients except the egg yolk, then use your fingertips to rub the butter into the flour. Stir in the yolk then switch to your hands to bring together and knead into a smooth dough.

Transfer the dough to a work surface, ideally covered with a silicone mat, and divide in half: use digital scales for accuracy.

Roll each piece into a cylindrical log 14 cm long and 3 cm in diameter. Flatten the ends.

Wrap each log in a separate piece of cling film and twist the ends to close. Hold the ends and roll each log up and down the work surface a few times to get it as smooth and even as possible.

Put the logs in the fridge for a minimum of 30 minutes until they're very firm. If you remember, turn the logs a couple of times to prevent a flat underside.

Logs can also be frozen at this point and defrosted overnight in the fridge.

Meanwhile, preheat the oven to 180°C /160°Fan /Gas 4 /350° F and lightly grease or line a baking tray.

Remove the dough from the fridge and unwrap.

Take a sharp knife and cut each log into 14 slices 1 cm thick.

Transfer to the prepared baking tray, leaving space between the biscuits to spread a little. Mix together the extra grated Parmesan and chopped rosemary then sprinkle over the biscuits.

Tip: if you want to prepare in advance, the shortbreads can be chilled again or frozen at this stage.

Put on a middle shelf of the oven and bake until light golden brown: approx. 15 - 20 min.

Transfer to a wire rack to cool where they'll firm up a little more.

To store: leave until completely cold before transferring to an airtight container. They will keep for up to a week or can be frozen.

Tip: can be eaten while still warm from the oven, or reheated for a few minutes in a low oven or air fryer, or approximately 30 seconds in a microwave.