01 - In a heatproof bowl, whisk the eggs and granulated sugar thoroughly until fully combined.
02 - Add the lemon zest and freshly squeezed lemon juice to the bowl and stir until blended.
03 - Place the bowl over a saucepan of gently simmering water, ensuring the base of the bowl does not touch the water.
04 - Whisk constantly over medium-low heat until the mixture thickens and coats the back of a spoon, approximately 8 to 10 minutes.
05 - Remove from heat and immediately whisk in the cubed unsalted butter until fully melted and the curd attains a silky consistency.
06 - Pour the lemon curd through a fine-mesh sieve into a clean bowl to eliminate zest pieces or any cooked egg bits.
07 - Let the curd cool, then transfer to sterilized jars. Refrigerate and use within two weeks.