Preheat the oven to 180ºc.
Cover a 9 x 13 inch baking tray with baking parchment. Leave an overlap and grease the parchment also.
Place the dry ingredients for the crust into a food processor and pulse to combine.
Add the cold butter and mix until it resembles coarse breadcrumbs around 10 seconds.
Pour the mixture into the prepared pan and press down. A measuring cup works well for pressing it flat and even.
Place in the fridge for 30 minutes or into the freezer for 15 minutes.
Bake in the oven for 15-20 minutes until the crust is golden.
Now to make the filling. In a large bowl whisk together the eggs, sugar, lemon juice, lemon zest and flour.
Remove the crust from the oven.
Pour the lemon mixture the top of the cooked base and immediately place the pan back into the oven and bake for a further 30-35 minutes until the topping is firm and set.
Allow to cool completely in the tin.
Once cooled using the overhang of parchment paper, lift out of the tin.
Cut into squares or triangles then dust with icing sugar.
Can be kept in an airtight container for four days in the fridge.
Can be frozen for three months.