01 - Wash lemons thoroughly. Finely zest all three lemons, then juice to yield approximately 1/2 cup of lemon juice.
02 - In a medium heatproof bowl, whisk together eggs, sugar, lemon zest, and lemon juice until fully blended.
03 - Place the bowl over a saucepan with gently simmering water, ensuring the bowl's bottom does not contact the water.
04 - Add cubed butter and sea salt to the mixture. Whisk continuously until thickened and coating the back of a spoon, about 10 to 15 minutes. Avoid boiling.
05 - Remove from heat and strain through a fine-mesh sieve into a clean bowl to achieve a smooth texture.
06 - Allow to cool slightly before transferring to sterilized jars. Refrigerate once cooled; curd will continue to thicken.