01 - In a heatproof bowl, whisk together eggs and granulated sugar until fully blended.
02 - Add lemon zest and lemon juice to the egg mixture, stirring until smooth.
03 - Set the bowl over a saucepan of gently simmering water, ensuring the bowl does not touch the water.
04 - Whisk constantly until the mixture thickens and coats the back of a spoon, approximately 8 to 10 minutes.
05 - Remove from heat and immediately whisk in cubed butter until fully melted and the curd is velvety smooth.
06 - Pour lemon curd through a fine-mesh sieve into a clean bowl to eliminate any zest or cooked egg residue.
07 - Allow to cool, then transfer to sterilized jars and refrigerate for up to two weeks.