Wash your lemons and grate the zest of each lemon. Squeeze and strain the juice of the lemons (measure 150ml).
In a large saucepan (or double boiler), place the lemon zest, lemon juice, butter and sugar. Warm gently, stirring all the time, until the butter has melted and the sugar has dissolved. Do not allow this mixture to boil.
In a separate bowl beat your eggs lightly. Add the eggs to the lemon mix and stir constantly with a wooden spoon.
If using a bain marie or double boiler, keep stirring the mixture, over the heat, as it gradually thickens to reach a coating consistency.
If you are doing this directly on the hob, make sure that your heat is turned to the minimum and keep stirring vigorously to prevent the mixture from over heating. This method is much quicker but be careful not to let the mixture boil or it will curdle.
Once the mixture reaches coating consistency pour into sterilized jars. In this case leave your jars to cool to room temperature before bottling as the heat of the jar will curdle your mixture otherwise.
Lemon curd must be kept in the fridge, and will last for 2-3 weeks. If you want to keep it longer, store in a plastic container in the freezer for up to 3 months.