Preheat oven to 180 C / 350 F. Grease and line a 16cm x 26cm slice pan with baking paper overhanging at the edges. Set aside.
To make the shortbread crust, place flour, sugar, butter and salt in a large bowl. Using a spatula, combine all the ingredients. Transfer this mixture into the slice pan. Press onto the base of the slice pan. Bake for 15-20 minutes or until lightly browned on the edges. Remove from oven. Set aside to cool.
Meanwhile, make the lemon layer. Whisk together sugar, flour and lemon zest in a large bowl until combined. Add eggs. Whisk until combined. Add lemon juice. Whisk again until combined.
Pour this mixture onto slightly cooled baked crust. Tap lightly to remove bubbles. Bake for 20-25 minutes or until set and slightly jiggly in the center.
Remove from oven. Allow to cool for about 1 hour. Refrigerate for another 2 hours.
Dust with confectioner’s (icing) sugar, slice and serve