Stir together the butter, sugar, egg yolk,
vanilla and zest from 1 lemon using a
wooden spoon. Stir in the flour – you
might need to get your hands in at the end.
Tip onto a floured surface, bring together
into a smooth dough, then roll out, half
at a time, and stamp out 5-6cm rounds.
Keep re-rolling trimmings, you should get
about 40 biscuits. Arrange on trays lined
with baking parchment, cover with cling
film and chill for 30 mins.