This is really scrumptious on scones or meringues
Place the sugar, cornflour and water in a large sauce pan and mix with a wooden spoon until smooth.
Stir in the lemon juice, egg yolks and salt.
Place on medium heat and keep stirring until the mixture starts to thicken and starts to bubble.
Stir in the lemon zest and the butter until the butter melts and remove the pan from the heat. Allow to cool and pour in jars.