You need 3 eggs, the juice and rind of 3 lemons, 100g of butter and 225g of caster sugar.
Melt the butter and sugar together in a bowl over a pan of boiling water. Then add the lemon rind and juice and the whisked eggs. Heat stirring now and then until it thickens, this takes about 25-30 mins.
Pour into sterilised jars, seal and label. This needs to be kept in the fridge and will last for about 3 months.