In food processor, blitz flour and sugar together.
Add lemon zest and butter and pulse until resembles bread crumbs.
Whisk the egg and vanilla together. Add to the dry ingredients and give the processor a couple of short pulses.
Transfer the pastry into a bowl and push it together with your hands so the dough comes together. Don’t handle for too long as you don’t want to melt the butter in the dough.
Wrap the dough in glad wrap and shape into a disc. Let it rest for ½ hr in the fridge before rolling it out.