01 - In a heatproof bowl, thoroughly whisk together eggs and granulated sugar until fully combined and smooth.
02 - Add the freshly grated lemon zest and lemon juice, stirring well to integrate.
03 - Place the bowl over a saucepan with gently simmering water, ensuring the bowl does not touch the water.
04 - Whisk the mixture continuously over medium heat until it thickens and coats the back of a spoon, approximately 8–10 minutes.
05 - Remove the bowl from heat and immediately add cubed butter, whisking until fully melted and the mixture is uniformly smooth.
06 - Pass the lemon curd through a fine-mesh sieve into a clean bowl to remove zest and any cooked egg bits.
07 - Allow the curd to cool, then transfer to sterilized jars. Refrigerate and consume within two weeks.