01 - Whisk together the eggs and granulated sugar in a heatproof bowl until homogenous.
02 - Blend in the lemon zest and freshly squeezed lemon juice.
03 - Place the bowl over a saucepan with gently simmering water, ensuring the bowl's base does not touch the water.
04 - Whisk the mixture constantly until it thickens and coats the back of a spoon, approximately 8 to 10 minutes.
05 - Remove the curd from heat and immediately whisk in the butter cubes until fully melted and the texture is smooth.
06 - Pass the lemon curd through a fine-mesh sieve into a clean bowl to remove zest or cooked egg particles.
07 - Allow the curd to cool, then transfer to sterilized jars and refrigerate for up to 2 weeks.