01 - Wash and zest 3 lemons, then juice to yield approximately 0.5 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 gently simmering water ensuring the bottom does not touch the water surface.
04 - Add cubed butter and a pinch of salt; whisk continuously until thickened and coating the back of a spoon, about 10 to 15 minutes without boiling.
05 - Remove from heat and strain through a fine-mesh sieve into a clean bowl to remove zest and cooked egg bits for a smooth consistency.
06 - Allow to cool slightly, then transfer to sterilized jars. Refrigerate until fully chilled and thickened.