Place plenty of water in a pot as well as half the cup of salt and bring to the boil. Add the samphire, leave it for 10 -15 seconds and then strain it. 

Pat the samphire dry using towels or kitchen paper and then place it in a jar. Mix the 3 tbsp of salt with one cup of water and add it to the jar with the samphire. Fill with vinegar and seal the jar. 

Store in a cool place. It is ready after a month.