In a saucepan, add in the egg yolks and the caster sugar, then whisk till smooth and combined

Zest and juice the orange, and add it to pot. Whisk till everything is combined

Turn on the gas to a medium heat, and cook slowly whilst stirring with a wooden spoon until the curd is thick enough to coat the back of a wooden spoon

Remove the pan from the heat and whisk in your cold butter, one cube at a time, until you end up with a thick and smooth curd

Leave to cool in the pot, then store in a sterilised glass jar up to a month