01 - In a heatproof bowl, vigorously whisk the eggs and granulated sugar until fully blended and slightly pale.
02 - Stir in the freshly grated lemon zest and lemon juice until evenly distributed.
03 - Place the bowl over a saucepan with gently simmering water, ensuring the bowl does not touch the water. Maintain a double boiler setup.
04 - Whisk the mixture constantly until it thickens and coats the back of a spoon, approximately 8 to 10 minutes.
05 - Remove the bowl from heat and immediately add butter cubes. Whisk until the butter is fully melted and the curd reaches a silky consistency.
06 - Transfer the lemon curd through a fine-mesh sieve into a clean bowl to eliminate any zest or coagulated egg. Allow to cool to room temperature.
07 - Pour cooled curd into sterilized jars and seal. Store in the refrigerator for up to two weeks.