Add the flour, cornflour, lemon zest and poppy seeds and mix well.
Work the dough with your hands to form a single mass.
Lightly flour a pastry board and roll out the dough to a thickness of about half a centimetre (roughly quarter of an inch).
Form biscuit shapes with a cutter or by hand and place on a non stick baking parchment on a baking tray.
Chill the uncooked shortbread for about 30 minutes.
To bake
Bake at 150C, 300F, gas mark 2 until just starting to turn golden at the edges. This may take around 20 minutes but check regularly to avoid overcooking.
Leave on the tray for about 5 minutes then transfer to a wire rack to cool.
Notes
NoteThe baking time above is based on baking in a single batch. To store
Store the shortbread in an airtight tin for up to a couple of days.
If you plan to keep them any longer it is better to freeze them and defrost when needed.
Tips
Remove the butter from the fridge ahead of starting to bake to allow it to soften.
Chill the lemon and poppy seed shortbread biscuits before baking to avoid spreading too much whilst in the oven.
Check regularly during the cooking time to avoid overcooking.