Grate and squeeze the juice out of the lemons.
Place the juice and zest in a pan with the butter and sugar. Heat until the sugar has dissolved and the butter has melted.
Add this mixture to the eggs gradually, stirring after each addition.
Pour back into the pan and place on medium heat again.
Heat the lemon curd while stirring continuously until the lemon curd thickens.
When the lemon curd coats the back of a wooden spoon, it is thick enough to be removed from the heat.
Place in a jam jar and leave to cool.
The curd will thicken as it cools, so don’t worry if it seems a bit runny at first.