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