Lemon curd

Whisk egg yolks and sugar until well combined but not frothy.

Tip into a heavy-based non-reactive saucepan and add butter, zest and juice.

Stirring constantly, bring to simmering point over a medium-high heat (about five minutes).

As soon as bubbles appear, remove from heat, still stirring. Allow to cool.

Transfer to sterilised jars and seal.