Preheat the oven to 180°C/160°C fan/350°F/gas mark 4. Grease a 23cm / 9inch square cake tin and line with baking parchment, making sure that you leave some overhanging so that you can easily lift the baked bars out of the tin.
Start by making the shortbread. Whisk together the softened vegan butter and the caster sugar with an electric mixer until it is light and fluffy, then whisk in the vanilla extract and a good pinch of salt.
Sift together the plain flour and cornflour (cornstarch) then add them to the butter mixture. Stir with a spatula until it forms a dough, it may seem like it is too much flour but it will combine eventually.
Tip the dough into the prepared cake tin and use your hands to pack it down as firmly and as evenly as possible.
Bake the shortbread for about 30 mins until it is golden brown. If it has puffed up at all press it back down gently.
While the shortbread is baking prepare the lemon curd. Place the cornflour in a non-reactive saucepan and gradually whisk in the water to make a smooth paste.
Whisk in the lemon juice, lemon zest, sugar, coconut cream, a pinch of salt and an optional pinch of turmeric.
When the shortbread is ready, place the pan over a medium heat and stir constantly until it comes up to the boil and thickens considerably.
Remove from the heat and add the butter, stir until it has dissolved then straight away pour the lemon curd over the baked (still warm) base.
Spread it level and leave to cool for 30 minutes then refrigerate for at least 2 hours before slicing into bars with a very sharp knife.