2) Cream the butter and beat in the sugar and lemon mixture. Add the eggs, one at a time, then add the lemon juice and salt. Mix until combined.
3) Pour the mixture into a 2L saucepan and cook over low heat until thickened, about 10 minutes, stirring constantly. The lemon curd will thicken at about 80C, or just below simmer.
4) Remove from the heat, pour into jars and cool or refrigerate.