01 - In a heatproof bowl, whisk together the eggs and granulated sugar until the mixture becomes smooth and fully combined.
02 - Add the freshly grated lemon zest and lemon juice to the bowl, and stir to integrate.
03 - Place the prepared bowl over a saucepan containing gently simmering water, ensuring the bowl does not touch the water’s surface.
04 - Whisk the mixture constantly over medium low heat until it thickens and coats the back of a spoon, approximately 8 to 10 minutes.
05 - Remove the bowl from the heat and immediately add the cubed butter. Continue whisking until the butter is fully melted, yielding a glossy, smooth curd.
06 - Pour the lemon curd through a fine-mesh sieve set over a clean bowl to remove any zest or cooked egg solids.
07 - Allow the curd to cool to room temperature, then transfer to sterilized jars. Refrigerate and use within two weeks.