01 - In a heatproof bowl, whisk together the eggs and granulated sugar until homogeneous.
02 - Stir in the lemon zest and lemon juice until fully integrated.
03 - Place the bowl over a saucepan of gently simmering water, ensuring the base does not touch the water.
04 - Whisk continuously, cooking until the curd thickens to coat the back of a spoon, approximately 8 to 10 minutes.
05 - Remove from heat and immediately whisk in butter cubes until melted and mixture is smooth.
06 - Pass the curd through a fine-mesh sieve into a clean bowl to ensure a smooth texture.
07 - Allow to cool, then transfer to sterilized jars. Refrigerate up to 2 weeks.