1. Scrub the lemons, grate the rind of two and squeeze the juice from all of them. 2. Whisk together eggs and sugar then add the juice and rind 3. Put mixture in a double boiler or bowl over a pan of hot water and add butter cut into small pieces. 4. Cook gently, stirring often, until the curd thickens (this may take up to 30 minutes) 5. Put into sterilised pots, keep cool and eat within a month.