Pre-heat oven: 180°C / 160°C (fan) / Gas Mark 4 / 350°F
Cream together the butter and sugar until fully combined.
Add in the vanilla extract and sift in the flour and mix together until a smooth dough forms.
Line a 9inch square baking tin with greaseproof paper and press the dough into the base of the tin, making sure to press firmly until you get an even layer. You can use your hands or the back of a large spoon.
Using a fork, poke little holes across the base to help it cook, then bake in the oven for 25mins until lightly golden.
While the base bakes, make the curd filling by sifting the flour into a large bowl and mixing with the sugar.
Beat in the eggs, lemon juice and zest until smooth.
Once the base has baked, pour the curd mix over the part-baked shortbread and bake for a further 18-20mins until very pale golden.
Allow the lemon bars to cool before cutting into slices. The bars will firm up as they cool.
Try swapping the 2 lemons for 3 limes for a twist on this classic.