1. Preheat oven to 160 degrees Celsius. 

2. Line a 23cms x 23cms baking tin with parchment paper.

3. Using a stand mixer, first cream the butter and lemon zest for a minute to really soften the butter. Then add the icing sugar and mix together until it is really soft, light and fluffy. ( 3 – 5 minutes)

4. In a separate bowl, sift the cornflour and flour and mix them together so they are evenly distributed. 

5. Add the flour to the butter and mix until it starts to clump and come together. At this point, stop mixing and use the warmth of your hand to bring the shortbread together. Do not over work.

6. Tip 2/3rds of the shortbread into the prepared tin and press it down firmly. 

7. I use a small piece of parchment and a small glass to roll the shortbread into each corner. This also ensures a flat, even base. 

8. Spread 6 tablespoons of lemon curd onto the base, taking care not to go right up to the edges. You want the lemon curd to not spill over and risk burning. 

9. Take the remaining shortbread and carefully make small, crumble sized pieces to layer on top of the lemon curd. Cover the  lemon curd completely so keep the pieces small. Press them into the lemon curd gently. 

10. Bake at 160 degrees Celsius for 30 – 35 minutes. The shortbread should JUST be starting to turn golden brown.

11. Remove from the oven and cool completely in the tin. Whilst it is still warm from the oven, score your squares but do not remove until completely cold.