Preheat oven to 190 c / 170 c fan / Gas mark 5 and line two large baking sheets with non-stick baking paper.
In a large mixing bowl, beat the butter or margarine with a hand whisk or an electric mix, or you could use a stand mixer, until soft.
Add in the flour a little at a time, while whisking the butter. Use a spatula to remove the mixture from the sides of the bowl.
Next, add the cornflour and sugar gradually.
Finally add the lemon juice and zest, along with the salt, whisking until the mixture all comes together into a ball of dough. It may seem a bit dry, but give it time, it can take a few minutes. Remove it from the bowl, then gently knead the last dry bits in by hand. Do not overmix.
On a lightly floured surface, sprinkle the dough with a little more flour, and roll to a thickness of about 5 or 6 mm. If you have trouble rolling it out smoothly, you can pop it in the fridge for 30 minutes, it may just be too warm.
Using a cookie cutter (mine is 7 cm / 2 ¾ inches, but a little bigger or smaller is ok) or a floured glass (if you don’t have a cutter) cut as many rounds as you can. Transfer each cookie to a prepared baking sheet. You should have between 12 and 16 cookies.
Bake for 20-25 minutes until the edges just begin to take a little colour, but keep an eye on them, you don’t want them to brown, they should be quite pale.
Let the cookies cool on the baking sheet for a few minutes, then move them onto a wire rack to finish cooling. Once cool dust with icing sugar.
Enjoy!
Notes
Once cool, store these vegan butter cookies in an airtight container or a cake or biscuit tin with a tight-fitting lid.They will keep for 2-3 days.Shortbread really is best when it's fresh.