Prepare Ingredients: Zest and juice the lemons, ensuring no bitter pith is included.
Mix Ingredients: In a heatproof bowl, combine lemon juice, zest, sugar, and butter. Crack the eggs and whisk until smooth.
Cook Over Bain-Marie: Place the bowl over a saucepan of simmering water, ensuring the water does not touch the bowl. Stir continuously for 10-15 minutes until the mixture thickens and coats the back of a spoon.
Strain and Store: Pour the curd through a fine sieve to remove zest and any solid bits. Transfer to sterilised jars and let cool completely before sealing.
Refrigerate: Store in the fridge for up to two weeks or freeze for up to three months.