Whisk egg yolks and castor sugar together in a medium-sized saucepan.
Add butter, lemon zest and lemon juice and stir mixture constantly over a very low heat for approximately 10 – 12 minutes or until mixture coats the back of a wooden spoon thickly.
Remove from stove and pour into sterilised jars, seal with a lid and place in the fridge to cool completely.
Recipe by Mrs Organised at http://www.mrsorganised.com.au/2015/03/28/lemon-curd/