01 - In a heatproof bowl, vigorously whisk together the eggs and granulated sugar until the mixture is fully blended.
02 - Stir in the lemon zest and freshly squeezed lemon juice, ensuring even distribution.
03 - Place the heatproof bowl over a saucepan of gently simmering water, making certain the base of the bowl does not touch the water.
04 - Continuously whisk the mixture over medium heat until it thickens and coats the back of a spoon, approximately 8 to 10 minutes.
05 - Remove the bowl from heat and immediately whisk in the unsalted butter, adding a few cubes at a time, until completely melted and the curd is smooth.
06 - Pass the lemon curd through a fine-mesh sieve into a clean bowl to remove any zest or coagulated egg for a silky texture.
07 - Allow the mixture to cool to room temperature. Transfer into sterilized jars and refrigerate for up to 2 weeks.