Preheat the oven to 180°C (350°F) and line 2 large baking trays with baking paper.
In a large mixing bowl, add in all of the white sugar and the lemon zest. Use your fingers to rub the zest into the sugar until fragrant. Scoop out ¼ cup of this lemon sugar and set it aside in a small bowl for rolling the cookie dough later.
Add the dairy free butter to the remaining sugar in the mixing bowl. Beat with an electric mixer on medium speed for 2–3 minutes, until light and fluffy.
Mix in the egg, vanilla extract, and lemon juice until fully combined. Scrape down the sides of the bowl as needed.
To the bowl, add in the plain flour, cornflour, baking powder, bicarbonate of soda, and salt.
Mix together on low speed until just combined. The dough should be soft but not sticky.
Using a cookie scoop or spoon, roll the dough into balls (about 1 ½ tablespoons each). Roll each ball in the reserved lemon sugar and place them 5 cm (2 inches) apart on a lined baking tray.
Place the cookies into the oven and bake for 10–12 minutes, or until the edges are set but the centres still look slightly soft.
Remove the tray from the oven and bang it on the counter a couple of times to help the cookies deflate slightly. If any cookies are misshapen, you can use a spoon to gently shape them back to a circle immediately after removing them from the oven.
Let the cookies cool on the tray for 5 minutes, then transfer to a wire rack to cool completely. You can store any leftovers in an airtight container for up to 5 days.