Make the pastry.
With your fingertips (or pulse using a food processor) rub together the butter, flour and icing sugar to form crumbs. Add the egg yolk and 1 – 2 tablespoons of ice cold water, bring together to make a dough. Do not overwork or it will toughen the pastry dough. Wrap in cling film and place in the fridge for at least 30 mins to rest.