Line 1 large or 2 regular sized baking trays with baking or greaseproof paper.

Use a zester or fine grater to remove the zest from the oranges.

Put the flour, sugar and salt in the bowl of a food processor and whizz briefly to combine.

Add the butter and process again until the mixture resembles breadcrumbs.

Add the orange zest (plus the orange extract if using) then process until a dough starts to form. Don't be tempted to add water: keep processing and the mixture will come together into a smooth, pliable dough.

Put the dough onto a clean worksurface or silicone mat, briefly knead to bring it together into a small ball, then divide in two.

Roll each piece into a cylinder 3 - 4 cm in diameter and flatten the ends.

Wrap each cylinder in a piece of cling film, twisting the ends to close (like a Christmas cracker). Holding the ends of the cling film, roll each cylinder up and down the work surface a few times to get it smoother.

Put the dough cylinders in the fridge for 30 minutes to firm up. If you remember to do it, turning a few times will prevent a flat underside

Can be chilled for longer or frozen if needed.

Meanwhile, preheat the oven to 170 C / 150 C Fan / Gas 3.

Remove the dough from the fridge and unwrap.

Take a sharp knife and cut off slices 5mm - 1cm thick: thinner will give you crisper biscuits, thicker for traditional, more tender shortbread.

Transfer to the prepared baking trays, leaving space for them to spread a little, and sprinkle each biscuit with a pinch of sugar if liked.

Biscuits can also be frozen at this stage.

Put the trays into the oven.

Bake until the biscuits are lightly golden and cooked all the way through. This should take 15- 20 minutes, depending on how thick you cut them.

Note that they may still be a little soft until cooler.

Leave the biscuits to cool on the tray for a few minutes then transfer to a wire rack to cool completely and firm up.

When cold, store in an airtight container.

Best eaten within 2-3 days.